PubMed Health⌕ Search

Biomedical subjects

C Hofmann

Publications and source records attributed to C Hofmann.

At least 37 records · Page 2Linked to original sources
PubMed1991

Glucose transport deficiency in diabetic animals is corrected by treatment with the oral antihyperglycemic agent pioglitazone.

Insulin-stimulated glucose uptake into muscle and fat involves regulation of the subcellular distribution and the expression of a specific facilitative glucose transporter protein (GLUT4). Peripheral glucose uptake is lowered in diabetes, and the expression of GLUT4 is depressed in animals that have been made diabetic (i.e. insulin deficient) by destruction of the pancreatic beta-cells. In the present study we found that GLUT4 expression is also decreased in an animal model for type II diabetes mellitus (noninsulin-dependent diabetes mellitus), KKAY obese mice. These KKAY mice have elevated circulating insulin levels, but target cell resistance to the metabolic actions of insulin. Treatment of both types of diabetic animals with pioglitazone, a new antihyperglycemic compound, corrects deficits in glucose transport and GLUT4 mRNA and protein abundance. Such corrections are, however, more readily detected in fat than in muscle. Increases in GLUT4 mRNA and protein levels and glucose transport function by pioglitazone are dependent upon the presence of circulating insulin. Treatment with pioglitazone alone is sufficient for correction of glucose transport in hyperinsulinemic insulin-resistant animals, but hypoinsulinemic animals require insulin therapy along with pioglitazone treatment for similar corrections. In these insulin-deficient animals, neither treatment with the drug alone nor minimal insulin replacement therapy results in substantial correction. Since insulin and this antihyperglycemic agent seem to work synergistically, it is likely that pioglitazone acts to amplify cellular responses to insulin.

Administration, Oral↗
PubMed1991

A rapid, accurate, nonradioactive method for quantitating RNA on agarose gels.

In order to study quantitative gene expression with Northern blots, it is important to have an internal standard that can be used to verify even loading or to correct for uneven loading between lanes. In this study it is shown that two-dimensional quantitation of ethidium bromide-intercalated 28S rRNA fluorescence can be used for such standardization. It was found that the film response of the fluorescence was linear with respect to total loaded RNA in the range of 2.5-12.5 micrograms RNA under the conditions used, after which the linear relationship falls off. This method eliminates the use of radiation for internal standardization of Northern blots.

3T3 Cells↗
PubMed1989

Monoclonal antibodies to the human insulin receptor mimic a spectrum of biological effects in transfected 3T3/HIR fibroblasts without activating receptor kinase.

The effects of four monoclonal antibodies to the alpha subunit of the human insulin receptor were studied in transfected mouse 3T3 fibroblasts expressing human insulin receptors (3T3/HIR). Three antibodies, MA-5, MA-20, and MA-51, mimicked insulin stimulation of the uptake of both 2-deoxy-D-glucose and alpha-aminoisobutyrio acid, and S6 kinase activity. Antibody MA-5 also mimicked insulin stimulation of [3H]thymidine incorporation and cell growth. Although these antibodies mimicked insulin stimulation of biological effects, they failed to significantly activate insulin receptor tyrosine kinase activity. These studies suggest, therefore, that the insulin receptor can signal a variety of cellular functions without stimulation of receptor kinase activity.

Aminoisobutyric Acids↗
PubMed1989

The metabolic and mitogenic effects of both insulin and insulin-like growth factor are enhanced by transfection of insulin receptors into NIH3T3 fibroblasts.

Insulin and insulin-like growth factor (IGF-I) have 50% sequence homology and regulate similar cellular functions. Their membrane receptors also share 84% homology in a tyrosine kinase domain essential to transmembrane signaling and may thus share common postreceptor paths. To probe action mechanisms for these related hormones, we examined the receptor and postreceptor overlap of responses stimulated by insulin and IGF-I. NIH3T3 mouse fibroblasts have few endogenous insulin receptors and are insensitive to insulin; they have IGF-I receptors and are responsive to IGF-I. Stable transfection of these cells with cDNA for the human insulin receptor yielded a cell line (3T3/HIR) expressing greater than 6 x 10(6) receptors/cell that was highly sensitive and responsive to insulin for stimulation of deoxy[14C]glucose uptake and [3H]thymidine incorporation. The cells also showed increased responses to IGF-I, although the sensitivity was less than that for insulin. The receptor specificity of such responses was examined with a monoclonal antibody MA10 that bound to insulin receptors, but elicited no responses. When 3T3/HIR cells were preincubated with MA10, subsequent insulin- or IGF-I-stimulated deoxy[14C]glucose uptake was markedly inhibited. Likewise, the presence of MA10 caused a 10-fold increase in the concentration of insulin needed to stimulate half-maximal incorporation of [3H]thymidine and also led to diminished IGF-I-stimulated responses. These results showed that the transfected human insulin receptors coupled readily with existing effector pathways in the mouse fibroblasts and mediated metabolic and mitogenic responses to both insulin and IGF-I. Such findings indicate that insulin and IGF-I regulate common cellular functions using both overlapping receptor and postreceptor signaling pathways.

Animals↗
PubMed1989

Human insulin receptors expressed in insulin-insensitive mouse fibroblasts couple with extant cellular effector systems to confer insulin sensitivity and responsiveness.

When cDNA for human kidney insulin receptors was used to transfect NIH3T3 mouse fibroblast cells with few or no endogenous insulin receptors, a resultant cell line, 3T3/HIR, expressed more than 6 million receptors/cell. Results of the present study demonstrated that these human receptors in murine cells mediated a diverse group of responses, including insulin binding and internalization as well as insulin-stimulated tyrosine phosphorylation of the receptor and a putative cellular substrate pp185. In addition, the cells were stimulated by insulin in various acute and long term metabolic processes, including glucose transport, glycogen formation, amino acid uptake, and thymidine uptake and incorporation into DNA. There were weak or no responses to insulin in control fibroblasts transfected only with the pSV2Neo plasmid containing a bacterial gene for neomycin resistance (3T3/NEO cells). These findings indicated that transfection of insulin receptor cDNA conferred insulin sensitivity to the target cells in a broad range of cellular responses and further demonstrated that effector molecules for mediating such responses were present in cells that normally lacked sensitivity to this hormone. Expressed receptors readily coupled with the effector systems to become fully functional.

Amino Acids↗
PubMed1989

Altered TSH levels associated with increased serum 1,25-dihydroxyvitamin D3: a possible link between thyroid and parathyroid disease.

The physiologic relationship between the thyroid and parathyroid glands remains poorly understood. A high incidence of coexistent thyroid disease and primary hyperparathyroidism has been well documented. Elevation of serum 1,25-dihydroxyvitamin D3 (vitamin D) has been detected in some patients with primary hyperparathyroidism. A report of specific binding sites and uptake of vitamin D by the thyrotrophs of the anterior pituitary indicates that vitamin D may modulate production or secretion of thyroid-stimulating hormone (TSH). To test this concept, we investigated the influence of elevated serum levels of vitamin D on basal and stimulated TSH. Vitamin D was administered by subcutaneously implanted sustained-release pellets at four dosages. Thyrotropin releasing hormone (TRH) stimulation tests were performed at time zero, 72 hours, 1 week, 2 weeks, and 5 weeks. Animals administered vitamin D became significantly hypercalcemic and demonstrated elevations of vitamin D, which peaked at 72 hours and remained elevated for 2 weeks after pellet implantation. TRH-stimulated TSH levels were significantly elevated at 72 hours and at 1 week and returned to normal after 5 weeks. Parathyroid hormone levels were suppressed at 72 hours and at 1 week and displayed significant elevation at 2 weeks. These results provide in vivo evidence for an interaction and a possible regulatory role of 1,25 on pituitary TSH secretion and parathyroid function.

Animals↗
PubMed1988

Binding of the delta endotoxin from Bacillus thuringiensis to brush-border membrane vesicles of the cabbage butterfly (Pieris brassicae).

The insecticidal delta endotoxin of Bacillus thuringiensis was labeled with iodine-125. Brush-border membrane vesicles, prepared from the midgut epithelium of Pieris brassicae larvae, known to be highly susceptible to the toxin, and from a non-target tissue: the small intestine of rat, were examined for binding of 125I-toxin. The toxin was bound specifically only to insect vesicles. Its binding to the insect membrane system was competitively inhibited by 127I-toxin and non-iodinated toxin, whereas the binding of the 125I-toxin to the mammalian membrane system was not affected by unlabeled toxin. Vesicles of P. brassicae possess two individual binding-site populations for iodinated toxin with dissociation constants of 46 nM and 490 nM. The Hill coefficients of both sites were approximately 1 and the binding capacities were 0.2 pmol and 30 pmol/mg vesicle protein for the high and the low-affinity sites respectively. The estimation of the dissociation constant for non-iodinated toxin, using a competition experiment, revealed only one binding-site population which possessed a dissociation constant of 235 nM. It is concluded that this is the binding site for the native toxin. This site was sensitive towards treatment with proteases or mixed glycosidases. It is suggested that it is a protein or a glycoprotein.

Animals↗
PubMed1988

Specificity of Bacillus thuringiensis delta-endotoxins is correlated with the presence of high-affinity binding sites in the brush border membrane of target insect midguts.

Binding studies were performed with two 125I-labeled Bacillus thuringiensis delta-endotoxins on brush border membrane vesicles prepared from the larval midgut of the tobacco hornworm Manduca sexta or the cabbage butterfly Pieris brassicae. One delta-endotoxin, Bt2-protoxin, is a 130-kDa recombinant crystalline protein from B. thuringiensis subsp. berliner. It kills larvae of both insect species. The active Bt2-toxin is a 60-kDa proteolytic fragment of the Bt2-protoxin. It binds saturably and with high affinity to brush border membrane vesicles from the midgut of both species. The other delta-endotoxin, Bt4412-protoxin, is a 136-kDa crystalline protein from B. thuringiensis subsp. thuringiensis, which is highly toxic for P. brassicae, but not for M. sexta larvae. Bt4412-toxin, obtained after proteolytic activation of Bt4412-protoxin, shows high-affinity saturable binding to P. brassicae vesicles but not to M. sexta vesicles. The correlation between toxicity and specific binding is further strengthened by competition studies. Other B. thuringiensis delta-endotoxins active against M. sexta compete for binding of 125I-labeled Bt2-toxin to M. sexta vesicles, whereas toxins active against dipteran or coleopteran larvae do not compete. Bt2-toxin and Bt4412-toxin bind to different sites on P. brassicae vesicles.

Animal Population Groups↗
PubMed1988

Transfer of functional insulin receptors to receptor-deficient target cells.

Purified human insulin receptors incorporated into phospholipid vesicles have previously been shown to retain insulin binding as well as insulin-stimulated beta-subunit autophosphorylating activity. These vesicles were used as a vehicle to transfer receptors to the insulin receptor-deficient Madin-Darby canine kidney (MDCK) cell line. Fusion of control [14C] dioleoylphosphatidylcholine-labeled phospholipid vesicles with MDCK cells was found to be dependent on both the amount of time and the concentration of polyethylene glycol used for fusion. Optimal insulin receptor transfer, as determined by recovery of [125I]insulin binding, occurred when MDCK cells were incubated for 45 min at 37 C in the presence of 15% polyethylene glycol plus receptor-containing vesicles. Scatchard analyses for insulin receptor binding before and after vesicle fusion demonstrated no postfusion alteration in insulin receptor affinity and a 10-fold increase in the number of insulin receptors present in the MDCK cells. Fusion transfer of insulin receptors to MDCK cells rendered the cells sensitive to insulin (10-100 nM) for stimulation of glycogen synthesis. Chloroquine (0.1 mM) was found to block endosomal processing of receptor-bound [125I] insulin within 1 h. These findings indicate that insulin receptors function as dissociable units which can be inserted into target plasma membranes with resultant recoupling to cellular systems.

Animals↗
PubMed1987

[S-100 protein in non-pigmented melanocytic and neuro-ectodermal tumors of the conjunctiva].

Using an immunoperoxidase method, S-100 protein was localized in 51 nonpigmented or slightly pigmented nevi, eight malignant melanomas, three neurofibromas, and one neurilemmoma of the conjunctiva. Clinico-immunohistochemical correlations are presented. Cells of these neuroectodermal tumors contain S-100 protein. Epithelial invaginations arising from the conjunctival surface and lying between melanocytes are S-100 protein-negative. This facilitates the differential diagnosis of particularly amelanotic lesions of the conjunctiva. Immunohistochemical identification of the S-100 protein represents an improvement in current histochemical differential diagnosis of these tumors.

Conjunctiva↗
PubMed1987

Sex hormone modulation of serum TSH levels.

This study was undertaken to determine the effects of estrogen and testosterone on baseline and thyrotropin-releasing hormone (TRH)-stimulated serum thyroid-stimulating hormone (TSH) levels in rats. Seven groups of 20 rats each were studied: intact males (group I), intact females (group II), castrated males (group III), castrated females (group IV), castrated males with testosterone replacement (group V), castrated females with testosterone supplement (group VI), and intact females with testosterone supplement (group VII). Two weeks after initiation of these hormone treatments, blood samples for TSH levels were obtained before and 10 minutes after TRH injection. Testosterone levels were also determined to verify hormone release. The results of these studies indicated that (1) testosterone has a primary, stimulatory role in the control of TSH concentration in that it causes elevation of both baseline and TRH-stimulated TSH levels, (2) endogenous estrogens have no such direct effect on TSH levels, and (3) in the presence of testosterone, endogenous estrogens partially inhibit the TSH-elevating effect of the androgen. As TSH stimulation is considered requisite for thyroid carcinogenesis, the different effects of testosterone and estrogen on TSH levels, demonstrated in this study, may in part explain differences in incidence and prognosis of thyroid carcinoma observed between the sexes in both rats and human beings.

Animals↗
PubMed1987

4,5-Dimethylangelicin effects on lymphocytes with and without UV-radiation.

Compared to the linear derivative 8-methoxypsoralen (8-MOP) the angular structured furocoumarin 4,5'-dimethylangelicin (4,5'-DMA) causes smaller photosensitization effects (loss of viability, inhibition of phytohemagglutinin (PHA)-induced transformation rate and E-rosette formation of T-cells, respectively) on cultured human lymphocytes. When 4,5'-DMA or 8-MOP are added to the cultures without additional UV-irradiation, increased or decreased PHA-stimulation rates are observed, respectively. In addition, 4,5'-DMA is able to reduce the binding of sheep erythrocytes to lymphocytes in a higher degree than 8-MOP. These findings suggest different action mechanisms on cytoplasma membranes and intracellular structures of lymphocytes by different furocoumarins.

Animals↗
PubMed1987

Radioiodine sensitivity of parafollicular C cells in aged Long-Evans rats.

An earlier study from our laboratory demonstrated that the incidence of thyroid C cell neoplasia in aging Long-Evans rats was high. When radioactive iodine was administered to 8-week-old Long-Evans rats, this incidence was reduced, although thyroid follicular cell neoplasia was increased. The aim of this study was to determine whether iodine-131 (131I) administered to an aged population of Long-Evans rats with established C cell hyperplasia would have a C cell ablative effect as pronounced as that observed in studies of young rats. For this study, 180 18-month-old Long-Evans rats (90 male and 90 female) were used. Baseline serum calcitonin levels were determined, and control and experimental groups containing equal numbers of animals were designated. 131I was administered by intraperitoneal injection to the experimental group, while equal volumes of saline solution were given to the control group. Blood samples for determination of serum calcitonin levels were obtained at 6-week intervals until the rats were 24 months old. Thyroid glands were then removed, and tissues were fixed, sectioned, and stained with hematoxylin and eosin and with peroxidase-antiperoxidase (PAP) using an anticalcitonin antibody. Examination of thyroid tissues showed that the incidence of C cell neoplasia was significantly reduced in irradiated animals as compared with nonirradiated controls (chi 2 analysis, p less than 0.05). PAP staining demonstrated diminished intracytoplasmic calcitonin in the radiation-treated group. Analysis of serum calcitonin levels over time showed significantly lower levels in the irradiated rat group than in the nonirradiated group (p less than 0.006).

Aging↗
PubMed1986

Binding and activity of Bacillus thuringiensis delta-endotoxin to invertebrate cells.

Fluorescein isothiocyanate was used as a label to detect delta-endotoxin of Bacillus thuringiensis subsp. thuringiensis and israelensis in binding studies with different in vitro cell systems. Protoxin of the subspecies thuringiensis could be labelled directly whereas the activated toxin had to be traced indirectly with labelled antibodies. Both protoxin and activated toxin bound to primary midgut cell cultures of Pieris brassicae larvae as well as to cells of an established culture of Drosophila melanogaster. No binding with either toxin form could be observed with hemocytes of P. brassicae. Biological activity as shown by the trypan blue viability assay was obtained only with the activated toxin against the midgut cells. Toxin of the subspecies israelensis reacted very unspecifically. Binding followed by rapid destruction was obtained with all the tested cultures.

Animals↗