G. Siegel

The antiatherosclerotic effect of Allium sativum

In a randomized, double-blind, placebo-controlled clinical trial, the plaque volumes in both carotid and femoral arteries of 152 probationers were determined by B-mode ultrasound. Continuous intake of high-dose garlic powder dragees reduced significantly the increase in arteriosclerotic plaque volume by 5-18% or even effected a slight regression within the observational period of 48 months. Also the age-dependent representation of the plaque volume shows an increase between 50 and 80 years that is diminished under garlic treatment by 6-13% related to 4 years. It seems even more important that with garlic application the plaque volume in the whole collective remained practically constant within the age-span of 50-80 years. These results substantiated that not only a preventive but possibly also a curative role in arteriosclerosis therapy (plaque regression) may be ascribed to garlic remedies.

Anionic biopolymers as blood flow sensors

The finding of flow-dependent vasodilation rests on the basic observation that with an increase in blood flow the vessels become wider, with a decrease the vascular smooth muscle cells contract. Proteoheparan sulphate could be the sensor macromolecule at the endothelial cell membrane-blood interface, that reacts on the shear stress generated by the flowing blood, and that informs and regulates the vascular smooth muscle cells via a signal transduction chain. This anionic biopolyelectrolyte possesses viscoelastic and specific ion binding properties which allow a change of its configuration in dependence on shear stress and electrostatic charge density. The blood flow sensor undergoes a conformational transition from a random coil to an extended filamentous state with increasing flow, whereby Na+ ions from the blood are bound. Owing to the intramolecular elastic recoil forces of proteoheparan sulphate the slowing of a flow rate causes an entropic coiling, the expulsion of Na+ ions and thus an interruption of the signal chain. Under physiological conditions, the conformation and Na+ binding proved to be extremely Ca(2+)-sensitive while K+ and Mg2+ ions play a minor role for the susceptibility of the sensor. Via counterion migration of the bound Na+ ions along the sensor glycosaminoglycan side chains and following Na+ passage through an unspecific ion channel in the endothelial cell membrane, the signal transduction chain leads to a membrane depolarization with Ca2+ influx into the cells. This stimulates the EDRF/NO production and release from the endothelial cells. The consequence is vasodilation.

Blood-flow sensing by anionic biopolymers

Abstract Using 23 Na-NMR techniques we could show that the polyanion proteoheparan sulfate integrated into the membrane of endothelial cells may serve as ‘flow sensor’. Based on its viscoelastic properties, heparan sulfate proteoglycan is present as a random coil under ‘no flow’ conditions, whereby most of its polyanionic sites undergo intramolecular hydrogen bonding. With increasing flow the macromolecule becomes unfolded into a filamentous structure. Additional anionic binding sites to which Na + ions from the blood bind are released by this shear stress-dependent conformational change. The Na + binding triggers the signal transduction chain for a vasodilatory vessel reaction. Decrease in flow effects, for reasons of the intramolecular elastic recoil forces of the macromolecules, an entropic coiling, the release of Na + ions and thus an interruption of the signal chain. Proteoheparan sulfate adsorbed onto a hydrophobic surface in physiological Krebs solution at pH 7.3 demonstrated clearly its characteristic as a Na + sensor. While Ca 2+ ions modulated the adsorption (promotion with increasing Ca 2+ concentrations) by changing the conformation of the sensor molecule, the adsorbed amount was determined preferably by the Na + concentration. K + and Mg 2+ ions showed slightly desorbing properties with increasing concentrations. Thus, it may be concluded that Na + ions play the role as ‘first messenger’ in flow-dependent vasodilatation.

The role of the endothelium in inflammation and tumor metastasis

In inflammation, cells interact with extracellular matrices or neighboring cells by a spatio-temporal intervention pattern of specific cell surface receptors and adhesion molecules. Resident cells of the injured tissue communicate with circulating effector cells by cytokines and direct cell-cell contact. These cytokines stimulate expression of the adhesion molecules ICAM-1, VCAM-1, and E- and P-selectin on endothelial cell surfaces and upregulate beta 2-integrins and ICAM-1 on luminal leukocytes. White blood cells then adhere to the activated endothelial cells, migrate through the vessel wall, and penetrate areas of infection or tissue damage. The basis for a cellular immune response is formed by the interaction between T lymphocytes and antigen-presenting cells amplified by adhesion molecule LFA-1,2,3 to ICAM-1 binding.

Omega-3 fatty acids: Benefits for cardio-cerebro-vascular diseases

BACKGROUND AND PURPOSE Intracranial artery stenosis (ICAS) is a narrowing of an intracranial artery, which is a common etiology for ischemic stroke. In this commentary, we review key aspects of the discrimination between non-stroke controls and ischemic stroke patients on the background of phospholipid ω3-fatty acid (DHA, EPA) composition. The discussion is embedded in the presentation of general effects of long-chain ω3 polyunsaturated fatty acids (PUFAs) in cardio-cerebro-vascular diseases (CCVDs) and Alzheimer dementia (AD). SUMMARY OF COMMENTARY ICAS is a common stroke subtype and has emerged as a major factor in recurrent stroke and vascular mortality. DHA and EPA are important fatty acids to distinguish between NCAS (no cerebral arteriosclerotic stenosis) and ICAS in stroke. The risk of ICAS is inversely correlated with the DHA content in phospholipids. Furthermore, a mechanistic explanation has been proposed for the beneficial effects of PUFAs in CCVDs and AD. CONCLUSIONS Whereas the beneficial effects of EPA/DHA for cardiovascular diseases and stroke seem to be beyond question, preventive effects in patients with very mild cognitive dysfunction and beginning Alzheimers disease undoubtedly need confirmation by larger clinical trials. A collaborative international basic science approach is warranted considering cautiously designed studies in order to avoid ethical problems.

23Na+NMR in solutions of mucopolysaccharides

Polyelectrolytes have a wide occurrence in biological systems and their function is greatly influenced by abundant small ions, for example, Na+, K’, Mg2* and Ca2+. The quadrupole relaxation method for studying ion binding to macromolecules, the principles of which are in [l] , should constitute a very general experimental approach to the problem of ion binding in biological systems. While the method has won wide-spread use in the field of protein chemistry [l-3] , ion binding to biological polyanions like nucleic acids [4,5], humic acids [6-91 and others [lo] has not been penetrated to the same depth. One reason for this is that in the case of proteins, it is much easier to isolate relaxation effects (e.g., using competition experiments) directly related to the biological function while this is not so for the polyanions. To be of any significant value, quadrupole relaxation studies of ion binding to polyelectrolytes must include studies of both longitudinal (T,) and transverse (TZ) relaxation times as a function of the degree of ionization. Even so the analysis is not without difficulties because several factors may influence the measured relaxation rates. However, a recent analysis [ 1 l] of rather extensive 23Na* relaxation data for a synthetic polyanion, polymethacrylic acid (PMA), gave consistent results and provides a suitable basis for the discussion of polyelectrolyte systems in general. Mucopolysaccharides, occurring in the extracellular matrix of connective tissues, form a group of biological polyanions for which the interactions with small cations is of great significance [12,13] ; e.g., there is certainly a critical interplay between ion binding phenomena and functionally important con-

Connective Tissue: More Than Just a Matrix for Cells

The general function of connective and supporting tissues consists, as the term implies, in the association of cells, the connection of the different tissues within the organs, the interrelation between the organs, and the shaping and posture of the whole body. As cartilage and bone tissues they have a supporting function, and as tendons, skin, and the fine network of the inner organs a stabilizing one [4]. Substances of the extracellular matrix play a decisive role in filtration, growth, and protease control through self-assembly, through formation of macromolecular structures of higher order, and through their interaction with cells. Above all, basement membranes of epithelial, endothelial, and muscle cells, complexly arranged and distinguished by their aggregated copolymeric compounds, are qualified for these biophysical and cell regulatory functions [237]. Through these, connective tissues participate indirectly in metabolic functions. Nutritive substances extravasated from the blood stream diffuse across the basement membrane and structural matrix elements to the cells to be supplied.

Ion transport and cation-polyanion interactions in vascular biomembranes☆

Abstract In arterial vascular smooth muscle, numerous effector influences, which guarantee the local regulation of blood flow by acting directly or indirectly on membrane polarization of the muscle cells, were tested. Variation of the extracellular hydrogen, norepinephrine or oxygen concentration alters the membrane potential of the smooth muscle cells and thus their tension, mainly via electromechanical coupling. The effect of H + ions can be primarily attributed to a change in Na + and K + permeability of the cell membrane, the effect of norepinephrine to a dose-dependent depolarization, and the effect of oxygen deficiency to an endogenous release of prostacyclin and endothelium derived relaxing factor resulting in membrane hyperpolarization. The sigmoid, stationary activation curve is independent of the nature of the effector influences operating preponderantly by voltage-dependent ion channels. It is the extent of the potential change induced by an effector which determines the variation in mechanical tension. The possibility of reversible ion binding to the polyanions of vascular connective tissues, which has not been previously reflected on within the context of membrane physiology of vascular smooth musculature, has been substantiated quantitatively by measurements with nuclear magnetic resonance spectroscopy. The change in effector ion concentrations can affect the conformation of cell membranous or membrane-vicinal, polyanionic proteoglycans. While monovalent cations exert merely a competitive interaction, divalent cations induce a conformational transition changing specifically the affinities for other ion species. Mg 2+ ions, for example, cause such a configurational change in the physiologic concentration range which promotes allosteric, cooperative binding of K + ions to vascular connective tissue. The geometry of narrow tissue clefts in the interstitial compartment of the vessel wall entails that an increase in extracellular Mg 2+ concentration effects a transient decrease in external K + concentration in the vicinity of vascular smooth muscle cell membranes. Membrane hyperpolarization and vasorelaxation are the result. The indirect action of divalent effector cations on vascular tone via variations in monovalent cation concentration of K + presents additional knowledge of the fundamental mechanisms of vasomotor regulations.

Cation-promoted adsorption of proteoheparan sulphate

Abstract The adsorption of proteoheparan sulphate, a strongly negatively charged proteoglycan, was investigated. It was found that heparan sulphate without any protein component does not adsorb in itself, either to hydrophilic or hydrophobized silica surfaces. Additions of excess electrolyte alone do not affect this behaviour. In the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB), however, adsorption occurs, presumably as polyelectrolyte-surfactant complexes. In the presence of excess electrolyte, the tendency for adsorption of the polyelectrolyte-surfactant complex is strongly increased. However, this effect cannot be satisfactorily explained by electrostatics alone. The native proteoheparan sulphate, however, does adsorb at hydrophobic surfaces, presumably via the hydrophobic domains of its protein core. On addition of CaCl 2 , the adsorbed amount increases strongly, analogous to the CTAB-heparan sulphate complex. For both proteoheparan sulphate and the CTAB-heparan sulphate complex, the adsorption and desorption processes are slow and the desorption on dilution is far from complete.

Local regulation of blood flow.

H+ and K+ ions participate decisively in the local regulation of blood flow. Variation of their extracellular concentration changes the membrane potential of vascular smooth muscle cells and tension via electromechanical coupling. The effect of K+ ions can be primarily attributed to a change of K+ equilibrium potential and electrogenic pump rate, the effect of H+ ions to a change of Na+ and K+ permeability of the cell membrane. Shifts of external proton and/or cation concentrations cause changes of the binding properties of the polyanionic macromolecules in vascular connective tissue. Thus, the extracellular concentration of various cation species can very fast and drastically in the tight mesh-work of connective tissue fibres close to the membrane of vascular smooth muscle cells. Especially, the K+ adsorption with extracellular acidification as well as the cooperative K+ binding as consequence of a conformational change induced by Mg++ ions are of great importance for membrane hyperpolarization and vasodilatation.