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Biomedical subjects

W Krone

Publications and source records attributed to W Krone.

At least 127 records · Page 7Linked to original sources
PubMed1991

Increased melanogenesis in cultured epidermal melanocytes from patients with neurofibromatosis 1 (NF 1).

Melanocyte cultures from the normally pigmented skin of patients with neurofibromatosis 1 (NF 1) have a higher melanin content than those from the skin of healthy donors. An additional increase in the amount of melanin per cell was found in 5 out of 6 lines of melanocytes derived from café au lait macules of NF 1 patients. Omission of the tumor promoter phorbol-12-myristate-13-acetate from the culture medium brings about a comparable increase in the melanin content in all three kinds of melanocyte cultures. Cultures of NF 1 melanocytes show a higher tyrosine hydroxylase activity than those of control melanocytes, and incorporate larger amounts of dihydroxyphenylalanine than the latter. We conclude that melanogenesis in epidermis melanocytes is affected by defective alleles of the NF 1 gene. Our findings do not contradict the hypothesis that the defect underlying NF 1 impairs the inhibition of a wild-type RAS oncogene by interfering with the GTPase-activating function of the NF 1 gene product.

Adolescent↗
PubMed1991

The size of small polydisperse circular DNA (spcDNA) in angiofibroma-derived cell cultures from patients with tuberous sclerosis (TSC) differs from that in fibroblasts.

Cell cultures were derived from angiofibromas of three patients with tuberous sclerosis (TSC), from the unaffected skin of these patients, and from the skin of five healthy donors. The length distributions of the small polydisperse circular DNA (spcDNA) fraction of these cell cultures were then analyzed. Nearly half the spcDNA molecules from the angiofibroma cultures were longer than 0.4 micron, whereas only about 7% exceeded this threshold in the spcDNA preparations from the skin fibroblast cultures. The percentage of the larger size class of spcDNA showed an increase at higher numbers of in vitro passages in all three types of cultures, but this effect was much more conspicuous in the angiofibroma-derived cultures than in those from the skin fibroblasts. An age-dependent increase in the overall amount of spcDNA was only seen in the angiofibroma-derived cultures. Our earlier finding of elevated amounts of spcDNA in angiofibroma cultures was confirmed in cultures from an additional TSC patient.

Adult↗
PubMed1990

Cytogenetic studies in tuberous sclerosis.

A cytogenetic study was performed with cultures derived from peripheral blood, unaffected skin, and angiofibromas of four patients suffering from the sporadic form of tuberous sclerosis (TSC). Increased frequencies of unstable chromosomal anomalies were found in lymphocytes and in fibroblasts from unaffected skin of the patients. The slight increase of the overall rate of unstable anomalies observed in angiofibroma-derived cultures above that of lymphocytes and skin fibroblasts, respectively, could almost entirely be attributed to a higher frequency of dicentric chromosomes. Of the 17 facial angiofibromas from which a total of 20 cell cultures were established, nine showed a normal karyotype, while eight exhibited stable chromosomal rearrangements, among which 19 clonal types could be identified. Unbalanced forms of various translocations caused partial trisomies of the long arms of chromosomes 1, 3, 7, 10, and 15. There was no clustering of breakpoints to a particular chromosomal region, nor was one particular chromosome preferentially involved. Frequencies and kinds of rearrangements varied between cultures derived from different angiofibromas from the same patient and between different culture charges from the same tumor. Tetraploidy was not generally more abundant in the angiofibroma-derived cultures, but there were a few culture charges with exceedingly high rates of tetraploid cells. The occurrence of premature centromere disjunction (PCD), either affecting all chromosomes or only part of them in angiofibroma-derived cultures, first described in TSC by Scappaticci et al. could be confirmed.

Chromosome Aberrations↗
PubMed1990

Hyperlipidaemia and hypertension.

Hyperlipidaemia and hypertension are commonly found in the population and are independent risk factors for cardiovascular complications. The combined presence of hypertension and hypercholesterolaemia increases considerably the risk for cardiovascular complications. These high-risk patients have to be identified early and treated appropriately in order to avoid complications. The goal of antihypertensive therapy is to reduce the average levels of diastolic pressure to below 90 mm Hg and the systolic pressure to below 140 mm Hg. The goals set for lipid levels in these patients are total cholesterol less than or equal to 200 mg/dl, LDL cholesterol less than or equal to 135 mg/dl and triglycerides less than or equal to 200 mg/dl. The first step in the treatment of patients with both hyperlipidaemia and hypertension is to seek underlying causes and to take appropriate therapeutic measures for both diseases. Non-pharmacological treatment of these high-risk patients includes weight reduction, appropriate dietary measures including alcohol and salt restriction, cessation of smoking and increasing physical activity. If pharmacological antihypertensive treatment is needed, drugs without adverse effects on lipid and lipoprotein levels should be preferred. If, in addition to dietary measures, drug treatment is necessary to reduce high cholesterol levels, bile acid sequestrants are the drug of first choice at present. If long-term safety can be established for HMG CoA reductase inhibitors, these drugs will represent a major advance in the therapy of hypercholesterolaemia.

Antihypertensive Agents↗
PubMed1990

Evidence for rapid selection and deletion of HIV-1 subpopulations in vivo by V3-specific neutralizing antibody: a model of humoral-associated selection.

Emergence in two chimpanzees of HIV-1 HTLV-IIIB variants resistant to neutralization by the pre-existing antibody is described. Viruses isolated from the HTLV-IIIB gp120 vaccinated and challenged animal were more resistant to neutralization, had more heterogenic genomes and showed more pronounced antigenic drift as determined by serotypic neutralization analysis than viruses isolated from the naive infected animal, indicating immune pressure as the selective mechanism. The earliest selecting antibody population detected in the chimpanzees appeared to be conformationally dependent. This was demonstrated by its ability to neutralize only the most replication-competent sub-populations of the HTLV-IIIB inoculum strain, yet was found to bind a HTLV-IIIB common nonapeptide (IQRGPGRAF) derived from the gp120 isolate-specific 3rd variable domain (V3) also known to induce isolate-specific neutralization in multiple species. Each of the recovered isolates had become resistant to neutralization by both a monoclonal (0.5 beta) and polyclonal HTLV-IIIB gp120 V3-specific antibody by as much as 16 to 256-fold. Amplification of the V3 coding sequence by polymerase chain reaction and subsequent sequence analysis of the neutralization-resistant variants obtained from in vivo infected animals indicated that resistance to neutralization was conferred by changes outside the direct binding site for the selective neutralizing antibody. Further studies indicated that apparent neutralization-resistant variants, yielded after in vitro passage through chimpanzee and human peripheral blood mononuclear cell cultures void of HIV-specific antibody, result from the homogenic amplification of the more replication competent sub-population pre-existing in the original viral stock. These faster replicating sub-populations appear to dominate initially and therefore are the initial prime targets recognized by the chimpanzee humoral immune system upon infection in vivo and thus eliminated. The described finding of virus escape due to a conformationally-induced flexibility of the major neutralization epitope termed "conformational-V3 hypervariability", coupled to the known primary amino acid hypervariability of this epitope (V3) termed "linear-V3 hypervariability", may be all that is required by the virus to survive in an otherwise effective humoral immune system.

Amino Acid Sequence↗
PubMed1989

Restriction analysis of chromosomal sequences homologous to single-copy fragments cloned from small polydisperse circular DNA (spcDNA).

Restriction fragments from the fraction of small polydisperse circular DNA (spcDNA) were cloned in pBR322. The spcDNA was prepared from cell cultures derived from an angiofibroma of a patient with tuberous sclerosis (TS). Such cultures have been shown previously to contain increased amounts of spcDNA. Four cloned spcDNA fragments containing single-copy sequences were chosen to characterize the homologous chromosomal DNA segments by restriction analysis. When used as hybridization probes, these four fragments generate well-defined nonvariable patterns in the chromosomal DNA from healthy donors. The restriction patterns obtained with one of the fragments (D-C4) can best be interpreted by assuming the presence of two copies of the homologous sequences in chromosomal DNA. A second sequence, A-B4, occurs at least 30-50 times in the haploid human genome. In both cases the duplicated regions span relatively large segments of DNA.

Base Sequence↗
PubMed1989

Metabolic changes during antihypertensive therapies.

There is controversy whether various classes of antihypertensive drugs can reduce significantly cardiovascular morbidity and mortality in primary prevention. A failure to show this in many studies was attributed, at least in part, to deleterious effects of these drugs on lipid metabolism. Especially adrenergic antihypertensives cause marked effects on lipoprotein levels in plasma. A review of the literature revealed that beta-blockers increase triglycerides and VLDL (very low density lipoprotein)-cholesterol and may lower plasma HDL (high density lipoprotein) levels. In contrast alpha 1-adrenergic inhibitors like prazosin, doxazosin and terazosin lower triglycerides, total cholesterol, LDL (low density lipoprotein)- and VLDL-cholesterol and increase plasma HDL levels. The mechanisms by which alpha- and beta-blockers may produce the observed effects on plasma lipids and lipoproteins are not well understood. It has been shown in our laboratory that the activity of the LDL receptor of peripheral cells, a major determinant of cholesterol levels in plasma, is regulated by catecholamines via alpha 2- and beta 2-adrenergic receptors. Accordingly, blockade of these adrenoceptors with alpha- and beta-adrenergic antagonists can reverse the catecholamine effect. In addition these agents may affect lipoprotein lipase, lecithin cholesteryl acyltransferase and cholesterol ester hydrolase. These data may explain, at least in part, the plasma effects. However, long-term studies are needed to clarify the clinical value of antihypertensives with different metabolic profiles.

Adrenergic alpha-Antagonists↗
PubMed1988

[Hypoglycemia caused by insulinoma in diabetes mellitus].

An hyperglycaemic metabolic state disappeared and spontaneous hypoglycaemia occurred in a 58-year-old woman with non-insulin-dependent obese type II diabetes. Abnormal absence of the hunger response with provoked hypoglycaemia, increased serum insulin concentrations and reduced blood glucose/insulin ratio led to the diagnosis of pathological hyperinsulinism, which was found to be due to an insulinoma of the tail of the pancreas. After its excision the patient's carbohydrate metabolism returned to a mild type II diabetic state and there were no further hypoglycaemic attacks.

Adenoma, Islet Cell↗
PubMed1988

Increased amounts of small polydisperse circular DNA (spcDNA) in angiofibroma-derived cell cultures from patients with tuberous sclerosis (TS)

Much greater amounts of small polydisperse circular DNA (spcDNA) have been detected, in cell cultures derived from angiofibromas of six patients with tuberous sclerosis (TS) than in those from the skin of these patients or from the skin of 11 healthy donors. This observation could be confirmed by spreading the DNA of appropriate fractions from CsCl density gradients. The findings suggest the existence of a relationship between the chromosomal instability observed in angiofibroma cultures and the mobilization of spcDNA.

Adult↗
PubMed1988

Regulation of sterol synthesis by histamine in human mononuclear leukocytes: roles of H1- and H2-receptors.

The effect of histamine on sterol synthesis has been investigated in freshly isolated human mononuclear leukocytes from healthy subjects. Incubation of cells for 6 h in a medium containing lipid depleted serum led to a threefold increase in the incorporation of (14C)-acetate or tritiated water into sterols. Histamine 0.3 microM added to the incubation medium at zero time inhibited this induction by 35% with a sigmoidal log dose-effect curve. The receptors mediating this action were characterised pharmacologically by using selective H1- and H2-agonists and -antagonists. The H2-agonists impromidine and 4-methylhistamine mimicked the effect of histamine on sterol synthesis, the suppression being 42% and 31%, respectively, at a concentration of 1 microM. In contrast, the H1-agonist 2-pyridylethylamine did not affect the pathway. The H2-antagonist cimetidine (10 microM) but not the H1-antagonist mepyramine (10 microM) totally reversed the inhibition of sterol synthesis by histamine. The results provide evidence that sterol synthesis in human mononuclear leukocytes is regulated by histamine, which appears to act predominantly via H2-receptors.

Cimetidine↗
PubMed1988

Effects of antihypertensives on plasma lipids and lipoprotein metabolism.

There is good epidemiologic evidence that hypertension is associated with a high risk of cardiovascular disease. However, primary intervention trials have failed to demonstrate that a reduction in blood pressure in hypertensive patients reduces morbidity and mortality from cardiac events. Since various antihypertensive drugs adversely affect lipoprotein metabolism, these drugs may increase associated coronary risk and offset the beneficial effects of lowering blood pressure. This article reviews the effects of various antihypertensive drugs on plasma lipids, lipoproteins, and apolipoproteins. They can be summarized as follows: thiazide-type diuretics cause a marked elevation of plasma triglycerides and very low-density lipoprotein (VLDL) and minor increases in total cholesterol and low-density lipoprotein (LDL), but have little effects on high-density lipoprotein (HDL). The nonselective beta-blockers do not significantly affect total cholesterol and LDL, but increase total triglycerides and VLDL and decrease HDL. The changes in plasma lipids and lipoproteins caused by cardioselective beta-blockers and beta-blockers with intrinsic sympathomimetic activity are qualitatively similar but less pronounced. Calcium antagonists and angiotensin-converting enzyme inhibitors appear to have no significant effects on plasma lipids. alpha 1-Inhibitors reduce total triglycerides, total cholesterol, VLDL, and LDL and increase HDL. The possible mechanisms by which antihypertensive drugs affect cellular lipid metabolism (e.g., LDL receptor, lipid synthesis, lipoprotein lipase, lecithin cholesteryl acyltransferase, acylcholesteryl acyltransferase, and cholesteryl ester hydrolase) are described. The clinical significance of changes in blood lipids and cellular lipid metabolism caused by antihypertensive drugs is not yet totally clear. Nevertheless, before antihypertensive drug treatment is initiated, blood lipid levels should be measured to identify preexisting hyperlipidemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive Agents↗
PubMed1988

Opposite effects of insulin and catecholamines on LDL-receptor activity in human mononuclear leukocytes.

The mechanisms by which insulin and catecholamines affect low-density lipoprotein (LDL)-receptor activity were studied in freshly isolated human mononuclear leukocytes. Incubation of cells for up to 24 h in a lipid-free medium resulted in an increase in the specific binding, accumulation, and degradation of 125I-labeled LDL. Insulin stimulated the ability of the cells to bind, accumulate, and degrade the lipoprotein with high affinity, which may be caused by an increase in the LDL-receptor number without altering binding affinity. (-)-Epinephrine inhibited the specific binding, accumulation, and degradation of 125I-LDL. This effect appears to be mediated by a decrease in the number of LDL receptors and not by a change in the binding affinity. (-)-Norepinephrine, the unspecific beta-adrenergic agonist (-)-isoproterenol, and the beta 2-specific agonist terbutaline mimicked the effect of epinephrine on LDL-receptor activity. Catecholamines and beta-adrenergic agonists yielded sigmoidal log-concentration effect curves. The action of epinephrine was attenuated by the beta-antagonist (dl)-propranolol. These results demonstrate that insulin stimulates and catecholamines suppress the specific binding, accumulation, and degradation of 125I-LDL in human mononuclear leukocytes. The catecholamine action appears to be mediated by beta 2-adrenergic receptors. A suppression of LDL-receptor activity resulting from deficiency of insulin and elevated plasma catecholamine concentrations in uncontrolled insulin-dependent diabetic patients may contribute to the increased levels of LDL cholesterol observed in these patients.

Catecholamines↗
PubMed1988

Effects of prostaglandins on LDL receptor activity and cholesterol synthesis in freshly isolated human mononuclear leukocytes.

The effects of prostaglandin (PG) E1, PGE2, the stable prostacyclin analogue Iloprost, and PGF2 alpha on low density lipoprotein (LDL) receptor activity and cholesterol synthesis were investigated in freshly isolated human mononuclear leukocytes. Incubation of cells for up to 45 hr in a lipid-free medium resulted in an increase in the rate of cholesterol synthesis from [14C]acetate and the high affinity accumulation and degradation of 125I-labeled LDL. Addition of PGE1 in increasing concentrations to the incubation medium inhibited cholesterol synthesis and the specific accumulation and degradation of 125I-labeled LDL; at a concentration of 10 microM, the inhibitions were 61%, 70%, and 67%, respectively, after an incubation of 20 hr. The effects of PGE2 and Iloprost were similar. The action of the prostaglandins on LDL receptor activity appeared to be mediated by a decrease in the number of LDL receptors and not by a change in the binding affinity. The prostaglandins yielded sigmoidal log concentration-effect curves. In contrast, PGF2 alpha had no influence on cholesterol synthesis or LDL receptor activity up to a concentration of 10 microM. PGE1, PGE2, and Iloprost, but not PGF2 alpha, led to an increase in the concentration of intracellular cyclic AMP. Dibutyryl cyclic AMP mimicked the effects of the E-prostaglandins and Iloprost on the LDL receptor activity. The results suggest that PGE1, PGE2, and prostacyclin affect LDL receptor activity and cholesterol synthesis and, therefore, may play a role in the regulation of cholesterol homeostasis and in the development of atherosclerosis.

Acetates↗
PubMed1988

Cell culture studies on neurofibromatosis (von Recklinghausen). VI. No increased stimulation of cell proliferation by sera from neurofibromatosis patients.

The growth-stimulating activity of sera from 10 patients with von Recklinghausen neurofibromatosis (NF-1) was compared with that of sera from 10 age- and sex-matched healthy donors. Cell cultures derived from peripheral neurofibromas and from skin biopsies of healthy persons were used as indicator cells. Stimulation of 3H-thymidine incorporation increased with the clotting time of the blood samples, reaching a plateau at about 35 h with no decline of activity during the following 48 h. There was no difference between the stimulating activity of sera from the NF-1 patients and that of sera from the healthy donors with either type of indicator cells. This held true when the indicator cells were stimulated during the exponential growth phase or when serum-starved confluent cells were exposed to the various sera. Three NF-1 strains used as indicator cells during this investigation showed a significantly less vigorous response to both types of human sera and to fetal calf serum than the respective control strains. All human sera collected after 42 h clotting time were superior to fetal calf serum with both types of indicator cells.

Blood Proteins↗