Cellular and molecular mechanisms of alcohol-induced osteopenia

Alcoholic beverages are widely consumed, resulting in a staggering economic cost in different social and cultural settings. Types of alcohol consumption vary from light occasional to heavy, binge drinking, and chronic alcohol abuse at all ages. In general, heavy alcohol consumption is widely recognized as a major epidemiological risk factor for chronic diseases and is detrimental to many organs and tissues, including bones. Indeed, recent findings demonstrate that alcohol has a dose-dependent toxic effect in promoting imbalanced bone remodeling. This imbalance eventually results in osteopenia, an established risk factor for osteoporosis. Decreased bone mass and strength are major hallmarks of osteopenia, which is predominantly attributed not only to inhibition of bone synthesis but also to increased bone resorption through direct and indirect pathways. In this review, we present knowledge to elucidate the epidemiology, potential pathogenesis, and major molecular mechanisms and cellular effects that underlie alcoholism-induced bone loss in osteopenia. Novel therapeutic targets for correcting alcohol-induced osteopenia are also reviewed, such as modulation of proinflammatory cytokines and Wnt and mTOR signaling and the application of new drugs.     

Cellular mechanisms and signals that coordinate plasma membrane repair

Plasma membrane forms the barrier between the cytoplasm and the environment. Cells constantly and selectively transport molecules across their plasma membrane without disrupting it. Any disruption in the plasma membrane compromises its selective permeability and is lethal, if not rapidly repaired. There is a growing understanding of the organelles, proteins, lipids, and small molecules that help cells signal and efficiently coordinate plasma membrane repair. This review aims to summarize how these subcellular responses are coordinated and how cellular signals generated due to plasma membrane injury interact with each other to spatially and temporally coordinate repair. With the involvement of calcium and redox signaling in single cell and tissue repair, we will discuss how these and other related signals extend from single cell repair to tissue level repair. These signals link repair processes that are activated immediately after plasma membrane injury with longer term processes regulating repair and regeneration of the damaged tissue. We propose that investigating cell and tissue repair as part of a continuum of wound repair mechanisms would be of value in treating degenerative diseases.     

Effects of pCai and pHi on cell-to-cell coupling

Internal longitudinal resistance (ri), a determinant of cardiac conduction, is affected by changes in intracellular calcium and protons. However, the role and mechanism by which H+ and Ca2+ may modulate ri is uncertain. Cable analysis was performed in cardiac Purkinje fibers to measure ri during various interventions. In some experiments, intracellular pH (pHi) was recorded simultaneously to study the pHi-ri relation. Both intracellular Ca2+ and H+ independently modified ri. However, internal resistance of cardiac fibers was insensitive to pHi changes compared to other tissues. A latent period preceded the pHi-related changes in ri and the amount of change depended upon methodology. The results suggest that direct action of protons or ri may be subordinate to other regulatory processes. Ionic regulation of internal longitudinal resistance may occur by more than one mechanism: i) direct cationic binding to sites on junctional membrane proteins; and ii) H+- or Ca2+-dependent phosphorylation of junctional proteins.     

Effects of pCai and pHi on cell-to-cell coupling

Summary Internal longitudinal resistance (r_i), a determinant of cardiac conduction, is affected by changes in intracellular calcium and protons. However, the role and mechanism by which H⁺ and Ca²⁺ may modulate r_i is uncertain. Cable analysis was performed in cardiac Purkinje fibers to measure r_i during various interventions. In some experiments, intracellular pH (pH_i) was recorded simultaneously to study the pH_i-r_i relation. Both intracellular Ca²⁺ and H⁺ independently modified r_i. However, internal resistance of cardiac fibers was insensitive to pH_i changes compared to other tissues. A latent period preceded the pH_i-related changes in r_i and the amount of change depended upon methodology. The results suggest that direct action of protons on r_i may be subordinate to other regulatory processes. Ionic regulation of internal longitudinal resistance may occur by more than one mechanism: i) direct cationic binding to sites on junctional membrane proteins; and ii) H⁺- or Ca²⁺-dependent phosphorylation of junctional proteins.     

The margin of overgrowth of the embryonic chick blastoderm as a study model for cell-to-cell contacts

Zusammenfassung Die Entwicklung vom «margin of overgrowth» junger Hühnerkeime ist verschieden nach Kontakt mit Helazellen und mit Mesonephros oder Hautgewebe; die ersteren hemmen die Entwicklung, die anderen werden vom Keim aufgenommen. Deshalb wird der «margin of overgrowth» als Modell für die Studie von Zellkontakten vorgeschlagen.     

Cellular pathology induced by snake venom phospholipase A2 myotoxins and neurotoxins: common aspects of their mechanisms of action

A large variety of snake toxins evolved from PLA₂ digestive enzymes through a process of ‘accelerated evolution’. These toxins have different tissue targets, membrane receptors and mechanisms of alteration of the cell plasma membrane. Two of the most commonly induced effects by venom PLA₂s are neurotoxicity and myotoxicity. Here, we will discuss how these snake toxins achieve a similar cellular lesion, which is evolutionarily highly conserved, despite the differences listed above. They cause an initial plasma membrane perturbation which promotes a large increase of the cytosolic Ca²⁺ concentration leading to cell degeneration, following modes that we discuss in detail for muscle cells and for the neuromuscular junction. The different systemic pathophysiological consequences caused by these toxins are not due to different mechanisms of cell toxicity, but to the intrinsic anatomical and physiological properties of the targeted tissues and cells. Received 05 March 2008; received after revision 08 April 2008; accepted 29 April 2008     

Accessibility of a critical prion protein region involved in strain recognition and its implications for the early detection of prions

Human prion diseases are characterized by the accumulation in the brain of proteinase K (PK)-resistant prion protein designated PrP27 – 30 detectable by the 3F4 antibody against human PrP109 – 112. We recently identified a new PK-resistant PrP species, designated PrP^*20, in uninfected human and animal brains. It was preferentially detected with the 1E4 antibody against human PrP 97 – 108 but not with the anti-PrP 3F4 antibody, although the 3F4 epitope is adjacent to the 1E4 epitope in the PrP^*20 molecule. The present study reveals that removal of the N-terminal amino acids up to residue 91 significantly increases accessibility of the 1E4 antibody to PrP of brains and cultured cells. In contrast to cells expressing wild-type PrP, cells expressing pathogenic mutant PrP accumulate not only PrP^*20 but also a small amount of 3F4-detected PK-resistant PrP27 – 30. Remarkably, during the course of human prion disease, a transition from an increase in 1E4-detected PrP^*20 to the occurrence of the 3F4-detected PrP27 – 30 was observed. Our study suggests that an increase in the level of PrP^*20 characterizes the early stages of prion diseases. Received 17 October 2007; received after revision 5 December 2007; accepted 14 December 2007     

Medicagenic acid,the factor responsible for hemolytic activity of lucerne saponins

Zusammenfassung Die aus Wurzeln von Luzerne isolierten Saponine wirken stärker hämolytisch als diejenigen in den grünen Teilen dieser Pflanze. Die hämolytisch wirksameren Saponine sind reicher an Medicagensäure und es wird angenommen, dass diese für die hämolytische Wirkung der Saponine verantwortlich ist. Die Anwesenheit von 2 Carboxylgruppen in der Medicagensäure scheint für ihre hämolytische Wirkung von ausschlaggebender Bedeutung zu sein, da der Dimethylester dieser Säure nicht mehr hämolytisch wirkt.

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This work was supported by Grant No. FG-Is-246 from the U.S. Department of Agriculture.     

Is serotonin or are its metabolites responsible for induction of hypothermia?

Summary Serotonin per se, rather than its metabolites, was shown to produce hypothermia in mice. This effect was mediated within the CNS and could be attenuated by methysergide.This study was supported in part by grants No. NS-12759 and No. AA-2696 from the USPHS and a research grant from the Graduate College of the University of Illinois.     

Substantivity and other factors responsible for formazan patterns in dehydrogenase histochemistry

Zusammenfassung Es wurden substantive Eigenschaften verschiedener Mono- und Ditetrazoliumsalze gegenüber Gewebebestandteilen im Schnittpräparat untersucht. Ditetrazole werden im allgemeinen stärker vom Gewebe adsorbiert als Monotetrazole. Ausnahmen bilden Monotetrazole mit polaren Substituenten oder Azobenzol-Resten in 3-Stellung. Ditetrazole mit elektronegativen Gruppen in 2-Stellung werden stark von Lipoprotein-Strukturen adsorbiert und zeigen in Modellexperimenten Substantivität für ungesättigte Lipoide. An verschiedenen Beispielen wird die Bedeutung substantiver Tetrazol-Eigenschaften für die Lokalisation von Dehydrogenaseaktivität im Schnittpräparat dargelegt. Die Lokalisation enzymatisch gebildeten Formazans ist im Falle von substantivem Tetrazol ein Ausdruck für die Adsorption der Farbstoffvorstufe an bestimmte Gewebekomponenten. Im Falle von nichtsubstantivem Monotetrazol besteht die Möglichkeit zur Bestimmung von Orten intrazellulärer Enzymaktivität ohne unspezifische Anfärbung von Gewebsbestandteilen. Die Bedeutung der stark voneinander abweichenden Eigenschaften von in der Histochemie gebräuchlichen Tetrazoliumsalzen für die Darstellung intra-und extramitochondrialer Aktivität wird diskutiert.

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Acknowledgments. We are indebted to ProfessorH. Beyer for the gift of MTT, to Dr.A. M. Seligman for Nitro-BT, to Dr.A. W. Nineham for M and B 1762 A and 1767 and to Dr.G. Glenner for BCT. We are grateful to Dr.G. Popják for assistance in the preparation of cell fractions. One of us (A. G. E. P.) is in receipt of a Grant in Aid from the Medical Research Council.