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Biomedical subjects

L H Block

Publications and source records attributed to L H Block.

At least 19 recordsLinked to original sources
PubMed1995

Platelet-derived growth factor stimulates the secretion of hyaluronic acid by proliferating human vascular smooth muscle cells.

Total glycans from the cell layer and the culture medium of human vascular smooth muscle cells (VSMC) that had been cultivated in the presence of platelet-derived growth factor (PDGF) were isolated and purified by gel filtration after Pronase and DNase digestion and alkaliborohydride treatment. Measurements of the content of neutral hexoses and uronic acids revealed that PDGF stimulates total glycan synthesis by proliferating VSMC in a linear fashion from 24 h to 72 h of incubation. In contrast, total glycan synthesis by human fibroblasts, epithelial cells, or endothelial cells was not affected by PDGF, indicating cell-type specificity. Chemical, biochemical, and enzymological characterization of the total glycans synthesized by VSMC showed that PDGF stimulates the secretion of a 340-kDa glycan molecule in a time-dependent manner from 24 h to 72 h. This molecule is highly acidic, shares a common structure with hyaluronic acid, and exhibits a potent antiproliferative activity on VSMC. These results suggest that VSMC in response to PDGF are capable of controlling their own growth and migration by the synthesis of a specific form of hyaluronic acid with antiproliferative potency, which may be involved in the regulation of the local inflammatory responses associated with atherosclerosis.

Amino Acids↗
PubMed1993

Transcriptional activation of low density lipoprotein receptor gene by angiotensin-converting enzyme inhibitors and Ca(2+)-channel blockers involves protein kinase C isoforms.

The pharmacological potency of angiotensin-converting enzyme (ACE) inhibitors (lisinopril and enalaprilat) on the transcription of low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl-CoA reductase genes was examined in human vascular smooth muscle cells and compared with the action of Ca(2+)-channel blockers (manidipine, verapamil, and diltiazem). Analogous to Ca(2+)-channel blockers, nanomolar concentrations of enalaprilat or lisinopril stimulated the synthesis of low density lipoprotein receptor mRNA and amplified the transcription induced by recombinant platelet-derived growth factor BB. In contrast to Ca(2+)-channel blockers, ACE inhibitors did not alter the transcription of the 3-hydroxy-3-methylglutaryl-CoA reductase gene. Platelet-derived growth factor BB stimulated the translocation of delta and epsilon isoforms of protein kinase C. Similar to Ca(2+)-channel blockers, ACE inhibitors reduced the translocation of delta and epsilon isoforms of protein kinase C. Furthermore, ACE inhibitors and Ca(2+)-channel blockers inhibited platelet-derived growth factor BB-induced transcription of c-fos and c-jun genes. The findings suggest that increased de novo synthesis of mRNA low density lipoprotein receptor apparently involves the participation of delta and epsilon isoforms of protein kinase C and transcription factors c-Fos and c-Jun.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Manidipine regulates the transcription of cytokine genes.

Manidipine, a Ca(2+)-channel blocker, at concentrations that lower elevated blood pressure, modulates the transcription rates of cytokine genes in the mesangial cells of humans that had been stimulated with platelet-derived growth factor BB isomer; although the transcription for mRNA of interleukin 1 beta and granulocyte/monocyte colony-stimulating factor was inhibited, the transcription of mRNA for interleukin 6 was enhanced. Additionally, the induction of c-fos, c-jun, and 3-hydroxy-3-methylglutaryl-coenzyme A reductase transcription was inhibited by manidipine. We conclude that manidipine, at nanomolar concentrations, is efficacious in modulating gene transcriptions that are involved in proinflammatory changes of mesangial cells. Thus, manidipine, at pharmacological concentrations that are one to two orders of magnitude lower than those required for inhibition of agonist- or depolarization (K+)-induced vasoconstriction, causes changes in the activity of the genes that code for inflammatory mediators.

Calcium↗
PubMed1992

Atherosclerosis, cell motility, calcium, and calcium-channel blockers.

Three key players in the humoral-cellular interactions that occur during the early development of atherosclerosis are presented as they activate platelets and vascular smooth muscle cells but eventually can be corrected by calcium-channel blockers. Platelet-activating factors via phospholipase C and phosphoinositides increase cytosolic calcium and phosphorylate contractile proteins, thereby inducing a change--aggregation and the secretory response of platelets. Low-density lipoprotein (LDL) has a similar hormone-like action and activates the signal transfer cascade that eventually leads to platelet aggregation as well as vascular smooth muscle cell proliferation. These effects can be greatly reduced by high-density lipoproteins. Platelet-derived growth factor stimulates the transcription of the LDL-receptor gene as well as the HMG-CoA reductase gene. The latter is inhibited by calcium-channel antagonists while the former is further enhanced. Thus, calcium-channel antagonists interfere with the stimulus-response coupling not only via slow calcium-channel influx inhibition but also by an additional membrane action and interference with gene activation.

Arteriosclerosis↗
PubMed1991

Ca(2+)-channel blockers modulate expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and low density lipoprotein receptor genes stimulated by platelet-derived growth factor.

The effects of Ca(2+)-channel blockers (amlodipine, nifedipine, nitrendipine, and verapamil) on expression of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (EC 1.1.1.88) and low density lipoprotein receptor (LDL-R) genes stimulated by recombinant platelet-derived growth factor BB isomer (PDGF-BB) were evaluated in human skin fibroblasts. The drugs enhanced expression of the LDL-R protein on the plasma membrane of the cells; in contrast, they inhibited expression of the HMG-CoA reductase gene. In addition, PDGF-BB-dependent stimulation of transcription of c-fos mRNA was inhibited also by the Ca(2+)-channel blockers. We conclude that PDGF-BB-dependent activation of the two genes is inhibited effectively by the Ca(2+)-channel blockers, at therapeutic concentrations, although they are unable to lower systemic cholesterol levels at these concentrations; however, they do modify responses of the two genes that are involved crucially in regulation of cellular cholesterol homeostasis.

Amlodipine↗
PubMed1991

Expressions of the low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl coenzyme A reductase genes are stimulated by recombinant platelet-derived growth factor isomers.

The plausible role that platelet-derived growth factor (PDGF) has in the localized pathophysiological changes that occur in the arterial wall during development of atherosclerotic lesions led us to investigate the influence of recombinant (r)PDGF isomers -AA, -AB, and -BB on the expression of low density lipoprotein receptor (LDL-R) and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase [(S)-mevalonate:NAD+ oxidoreductase (CoA-acylating), EC 1.1.1.88] genes. In addition, we clarified the role of protein kinase C (PKC) in expression of the two genes in human skin fibroblasts and vascular smooth muscle cells. The various rPDGF isoforms are distinct in their ability to activate transcription of both genes: (i) Both rPDGF-AA and -BB stimulate transcription of the LDL-R gene; in contrast, rPDGF-BB, but not -AA, activates transcription of the HMG-CoA reductase gene. (ii) All recombinant isoforms of PDGF activate transcription of the c-fos gene. (iii) While rPDGF-dependent transcription of the LDL-R gene occurs independently of PKC, transcription of the HMG-CoA reductase gene appears to involve the action of that enzyme.

Animals↗
PubMed1990

Physicochemical characterization of a polypeptide present in uremic serum that inhibits the biological activity of polymorphonuclear cells.

A granulocyte inhibitory protein was isolated and characterized from uremic serum by using ion-exchange column chromatography, high-performance size-exclusion chromatography, and immunochemical procedures. The purification process concentrated the protein 240-fold and to a purity of greater than 95%. An overall recovery of 45% was achieved; the purified protein had a specific activity of 104 units per mg of protein. The polypeptide had a molecular weight of approximately 28,000 and an isoelectric point of 4.0-4.5. Amino acid sequencing of the NH2 terminus revealed a single sequence (Asp-Ile-Val-Met-Thr-Gln-Ser-Pro-Gly-Thr-Leu-Ser-Val-Ser-Pro-Gly-Glu-Arg-Ala- Thr) that proved to be nonhomologous with other serum proteins that appear during an inflammatory state. The polypeptide inhibited the uptake of deoxyglucose, chemotaxis, oxidative metabolism, and intracellular bacterial killing by polymorphonuclear leukocytes. A specific rabbit polyclonal antibody raised against the protein nullified these inhibitory changes. We contend that the protein is responsible for the leukocyte dysfunction that is commonly seen in patients with uremia.

Amino Acid Sequence↗
PubMed1990

PAF-dependent phosphatidylinositol turnover in platelets: differences between asthmatics and normal individuals.

The effects of nebulized platelet-activating factor (PAF) on the pulmonary and cardiovascular systems, and on the platelets present in peripheral blood were investigated in 9 normal individuals and in 6 patients with asthma and 3 individuals with lyso-PAF. The inhalation of PAF caused an acute decrease in specific airway conductance. The circulatory system parameters monitored showed an increase in heart rate while blood pressure decreased in both groups that were studied. The inhalation of PAF led to a significant increase in the differential count of polymorphonuclear leukocytes after 15 min; the count returned to the initial level after 24 h. However, the platelet count remained unchanged. The phosphatidylinositol (PI) turnover and in particular the formation of 1,4,5-inositoltrisphosphate (IP3) in platelets were investigated after PAF inhalation. It also mediated an increase in intracellular free calcium concentration, [Ca2+]i, in response to a second challenge with exogenous PAF. The basal levels of IP3 and [Ca2+]i were significantly greater in the platelets of patients with asthma than in those of normal individuals (p less than 0.01). Platelets that had been isolated from normal and asthmatic subjects had a higher concentration of IP3 and [Ca2+]i in the platelets after an in vitro exposure to PAF. After an inhalation challenge with PAF, the platelets of both the normal individuals and the patients with asthma showed a specific refractoriness to the in vitro exposure to PAF. Perhaps, this is an explanation for the PAF-dependent tachyphylaxis that is commonly observed in both normal and asthmatic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1989

Ca2+-channel blockers inhibit the action of recombinant platelet-derived growth factor in vascular smooth muscle cells.

Human platelet-derived growth factor (PDGF) is mainly composed of two polypeptide chains (PDGF-AB). All three possible dimeric forms of PDGF--i.e., PDGF-AA, PDGF-BB and PDGF-AB--exist in nature. We have used two recombinant PDGF homodimers to determine the roles of each isoform in the activation of phosphatidylinositol turnover in vascular smooth muscle cells (VSMC) isolated from rat thoracic aorta, their mitogenic effect on VSMC, and their vasoconstrictor effect on intact strips of aortic vascular tissue. Three Ca2+-channel blockers, nifedipine, verapamil, and diltiazem, were used as antagonists for investigating the PDGF-dependent changes mediated by the homodimers. PDGF-BB had a greater efficacy than PDGF-AA on inositol 1,4,5-trisphosphate release, on the formation of diacylglycerol, and on Ca2+ mobilization, which was also associated with vasoconstrictor activity and effective mitogenicity. PDGF-AA, on the other hand, was more potent than PDGF-BB in stimulating protein kinase C. In all instances, the activation of the phosphatidylinositol turnover by the two homodimers was inhibited by the Ca2+-channel blockers.

Animals↗
PubMed1989

Platelet-activating factor (PAF)-dependent biochemical, morphologic, and physiologic responses of human platelets: demonstration of translocation of protein kinase C associated with protein phosphorylation.

Platelet-activating factor (PAF) is a potent stimulus for platelet aggregation and secretion. PAF has been shown to stimulate the phosphatidylinositol (PI) pathway in platelets, which implies that PAF should activate protein kinase C. In this study, measurements of PI metabolites, the elevation of intracellular free calcium concentration, (Ca2+)i, the activation of protein kinase C, and the phosphorylation of platelet proteins (using a two-dimensional gel electrophoretic technique) were performed before and after the addition of 10(-8) M PAF to human platelets. These findings were correlated with morphologic changes in the platelets as determined by immunoelectron microscopic studies on the cytoskeleton and by X-ray analysis of dense bodies. The results show that PAF stimulates the production of PI metabolites and causes an increase in the membrane-associated activity of protein kinase C. These changes are accompanied by a rise in the (Ca2+)i and protein phosphorylation. The increase in protein kinase C activity reaches a maximum at approximately 60 s, a time frame that is consistent with the protein phosphorylation and the subsequent morphologic and secretory events. X-ray analysis revealed two types of dense bodies containing various amounts of calcium which appeared to be released sequentially after PAF activation. These results suggest that the protein phosphorylation that controls the physiologic events resulting from PAF activation of human platelets is catalyzed by protein kinase C.

Actins↗
PubMed1988

Rapid activation of human platelets by low concentrations of low-density lipoprotein via phosphatidylinositol cycle.

The interaction of low-density lipoprotein (LDL) with the human platelet was investigated with regard to saturable high-affinity binding, shape change, cytosolic free Ca2+ concentration, phosphatidylinositol (PtdIns) turnover, and thromboxane B2 biosynthesis. The experiments show that LDL, at a concentration approximately 100 times lower than in plasma, causes platelet activation concomitantly with stimulation of the PtdIns cycle and thromboxane B2 formation, similarly to other activators of platelets. The effects of LDL were inhibited by high-density lipoprotein. The results suggest that activation of platelets by low concentrations of LDL may play a role in pathophysiological conditions and that platelet can serve as a model for studying the influence of LDL on various target cells.

Binding Sites↗
PubMed1988

Low density lipoprotein causes general cellular activation with increased phosphatidylinositol turnover and lipoprotein catabolism.

Low density lipoprotein (LDL), at concentrations high enough for receptor binding but not high enough to saturate the receptor, induces activation of phosphatidylinositol (PtdIns) turnover in a variety of cell types with various biological functions. Using both biochemical and electron microscopic studies, we have shown that blood platelets take up and degrade LDL in a manner reminiscent of phagocytic cell types. The activation of both PtdIns turnover and LDL metabolism is inhibited by high density lipoprotein. Thus, LDL at hormonal concentrations causes general cellular activation. Since all cell types studied responded to LDL with increased PtdIns turnover and uptake of LDL cholesterol, the PtdIns cycle may also be involved in the cellular regulation of LDL cholesterol metabolism.

Animals↗
PubMed1987

Diagnostic and prognostic value of RNA-proteolipid in sera of patients with malignant disorders following therapy: first clinical evaluation of a novel tumor marker.

The circulating level of a novel RNA-proteolipid complex associated with malignant diseases was critically evaluated as a tumor marker in clinical oncology. The complex, isolated from the sera of cancer patients, exhibited unvarying chemical composition regardless of the cell type and clinical staging. Clearance from blood was rapid with a half-life of approximately 2 days. Tumor mass could be correlated with the circulating level. After effective treatment the level fell and rose again 10 months prior to the conventional clinical diagnosis of relapse.

Biomarkers, Tumor↗
PubMed1987

Atherogenesis and hypertension.

Low-density lipoprotein (LDL) is essential for the regulation of cellular cholesterol homeostasis. Intracellular LDL cholesterol metabolism is achieved by the action of lysosomal enzymes. The hydrolytic cleavage of cholesterol is apparently suppressed in the smooth muscle of arterial vessels of hypertensive animal models, contributing to atherosclerosis. The change in the hydrolytic activity of the enzymes can be reversed by Ca2+ antagonists which also lower increased blood pressure. Thus, a blood pressure lowering effect of calcium antagonists may explain the antiatherosclerotic action of these agents. Preliminary data, using platelets as a model for studies on LDL action, suggest that LDL induces rapid cellular activation via phosphatidylinositol turnover.

Acetylglucosaminidase↗