Transgenic nonhuman primates for neurodegenerative diseases

Animal models that represent human diseases constitute an important tool in understanding the pathogenesis of the diseases, and in developing effective therapies. Neurodegenerative diseases are complex disorders involving neuropathologic and psychiatric alterations. Although transgenic and knock-in mouse models of Alzheimer's disease, (AD), Parkinson's disease (PD) and Huntington's disease (HD) have been created, limited representation in clinical aspects has been recognized and the rodent models lack true neurodegeneration. Chemical induction of HD and PD in nonhuman primates (NHP) has been reported, however, the role of intrinsic genetic factors in the development of the diseases is indeterminable. Nonhuman primates closely parallel humans with regard to genetic, neuroanatomic, and cognitive/behavioral characteristics. Accordingly, the development of NHP models for neurodegenerative diseases holds greater promise for success in the discovery of diagnoses, treatments, and cures than approaches using other animal species. Therefore, a transgenic NHP carrying a mutant gene similar to that of patients will help to clarify our understanding of disease onset and progression. Additionally, monitoring disease onset and development in the transgenic NHP by high resolution brain imaging technology such as MRI, and behavioral and cognitive testing can all be carried out simultaneously in the NHP but not in other animal models. Moreover, because of the similarity in motor repertoire between NHPs and humans, it will also be possible to compare the neurologic syndrome observed in the NHP model to that in patients. Understanding the correlation between genetic defects and physiologic changes (e.g. oxidative damage) will lead to a better understanding of disease progression and the development of patient treatments, medications and preventive approaches for high risk individuals. The impact of the transgenic NHP model in understanding the role which genetic disorders play in the development of efficacious interventions and medications is foreseeable.     

Succinate dehydrogenase : a partial purification from mung bean hypocotyls and soybean cotyledons

A procedure was developed for the partial purification of succinate dehydrogenase from mung bean (Vigna radiata L.) hypocotyls and soybean (Glycine max [L] Merr. v. Ransom) cotyledons. The procedure utilized a Triton X-100 extraction followed by ammonium sulfate precipitation. The final fraction was enriched in two polypeptides with approximate molecular weights of 67,000 and 30,000 daltons, exhibited a pH optima of 7.0 to 7.5, contained a b-type cytochrome, and exhibited the characteristic ferredoxin-type and high potential iron-sulfur protein-type electron paramagnetic resonance signals reported for the iron-sulfur centers of mammalian succinate dehydrogenase. Inhibition constants of 1.15 and 24.6 micromolar for oxaloacetate and malonate, respectively, were obtained.     

The antibacterial activity of human neutrophils and eosinophils requires proton channels but not BK channels

Electrophysiological events are of central importance during the phagocyte respiratory burst, because NADPH oxidase is electrogenic and voltage sensitive. We investigated the recent suggestion that large-conductance, calcium-activated K(+) (BK) channels, rather than proton channels, play an essential role in innate immunity (Ahluwalia, J., A. Tinker, L.H. Clapp, M.R. Duchen, A.Y. Abramov, S. Page, M. Nobles, and A.W. Segal. 2004. Nature. 427:853-858). In PMA-stimulated human neutrophils or eosinophils, we did not detect BK currents, and neither of the BK channel inhibitors iberiotoxin or paxilline nor DPI inhibited any component of outward current. BK inhibitors did not inhibit the killing of bacteria, nor did they affect NADPH oxidase-dependent degradation of bacterial phospholipids by extracellular gIIA-PLA(2) or the production of superoxide anion (O(2*)(-)). Moreover, an antibody against the BK channel did not detect immunoreactive protein in human neutrophils. A required role for voltage-gated proton channels is demonstrated by Zn(2+) inhibition of NADPH oxidase activity assessed by H(2)O(2) production, thus validating previous studies showing that Zn(2+) inhibited O(2*)(-) production when assessed by cytochrome c reduction. In conclusion, BK channels were not detected in human neutrophils or eosinophils, and BK inhibitors did not impair antimicrobial activity. In contrast, we present additional evidence that voltage-gated proton channels serve the essential role of charge compensation during the respiratory burst.     

The influence of Mg2+ on the phosphorylation and dephosphorylation of myosin by an actomyosin preparation from vascular smooth muscle

Previous work has shown that Mg²⁺ levels modulate the net level of myosin light chain phosphorylation in bovine aortic smooth muscle actomyosin preparations. The goal of this study was to determine the precise step, i.e. phosphorylation or dephosphorylation, where Mg²⁺ modulates the net phosphorylation reaction. The technique using [γ³⁵S]ATPγS to monitor the phosphorylating step yielded no effect of either Mg²⁺ or Ca²⁺. Unfortunately the lack of Ca²⁺-dependence did not allow conclusions about the influence of Mg²⁺ on myosin light chain kinase activity. The study of the effect of Mg²⁺ on dephosphorylation showed that phosphatase activity in the actomyosin preparation exhibited a Mg²⁺ modulation only when the actomyosin was previously exposed to activating levels (3×10^?5M) of Ca²⁺, suggesting the presence of a Ca²⁺ -regulation system for myosin light chain phosphatase.     

Organism-specific neutrophil-endothelial cell interactions in response to Escherichia coli, Streptococcus pneumoniae, and Staphylococcus aureus

The recruitment of polymorphonuclear leukocytes (PMNs) from the vascular space into the lung interstitium and airspace is an early step in the host innate immune response to bacterial invasion of these sites. To determine the ability of intact bacteria to directly elicit PMN migration across an endothelial monolayer, we studied in vitro migration of PMNs across a monolayer of human pulmonary microvascular endothelial cells in response to Streptococcus pneumoniae, Staphylococcus aureus, and Escherichia coli, as well as to purified E. coli LPS. Bacterial induction of PMN migration was dose dependent and elicited by > or =10(4) bacteria/ml of each of the species tested. Pretreatment of PMNs with blocking Abs to CD18 significantly inhibited migration of PMN in response to all stimuli tested, but had the most profound effect on migration to S. pneumoniae and S. aureus. Intact E. coli were 10 times more potent in inducing transmigration of PMNs than a corresponding amount of purified LPS. Bacterial induction of PMN migration did not correlate with up-regulation of surface endothelial ICAM-1 expression (purified LPS > intact E. coli > S. aureus and S. pneumoniae) nor up-regulation of VCAM-1 and E-selectin. Neutralizing Ab to ICAM-1 had no effect on PMN migration to any of the bacteria or to purified LPS. These findings demonstrate that diverse bacterial pathogens induce PMN migration across a pulmonary microvascular endothelial cell monolayer in a fashion that appears to be organism specific. In addition, intact bacteria elicit PMN-endothelial cell interactions distinct from those seen when purified bacterial products are used as agonists.     

Substrate based inhibitors of smooth muscle myosin light chain kinase.

Activation of myosin light chain kinase is a prerequisite for smooth muscle activation. In this study, short peptide analogs of the phosphorylation site of the myosin light chain were studied for their effects on several contractile protein systems. The peptides inhibited phosphorylation of isolated ventricular and smooth muscle myosin light chains by smooth muscle myosin light chain kinase, but they were only weak inhibitors of phosphorylation of intact myosin and actomyosin. The peptides were also unable to block force development or myosin light chain phosphorylation in glycerol permeabilized fibers of swine carotid media. Apparently, the association of the myosin light chain with myosin changes its conformation such that substrate analogs which are potent inhibitors of the phosphorylation of isolated myosin light chains by myosin light chain kinase are ineffective at blocking phosphorylation of the intact molecule.     

Enhancement of the autocatalytic activation of trypsinogen to trypsin by bile and bile acids

The activation of trypsinogen to trypsin in the small intestine can occur by the action of enterokinase or, alternatively, as an autocatalytic process catalysed by trypsin itself. We have found that bile salts and human bile cause a significant enhancement of the autocatalytic activation of trypsinogen. This effect is dependent on the calcium ion concentration and is most marked around pH 5.4 and 7.8. An optimum concentration exists for each bile salt at which the greatest enhancement occurs. At this concentration, certain bile salts have been shown to produce activation effects of up to 55-fold. It is suggested that this activation of the autocatalytic process by bile plays an important role in protein digestion in the small intestine, since it has been shown previously that duodenal trypsin levels are abnormally low in patients with an impairment of bile secretion.     

Phosphatidylinositol 3-kinase modulates vascular smooth muscle contraction by calcium and myosin light chain phosphorylation-independent and -dependent pathways

Regulation of smooth muscle contraction involves a number of signaling mechanisms that include both kinase and phosphatase reactions. The goal of the present study was to determine the role of one such kinase, phosphatidylinositol (PI)3-kinase, in vascular smooth muscle excitation-contraction coupling. Using intact medial strips of the swine carotid artery, we found that inhibition of PI3-kinase by LY-294002 resulted in a concentration-dependent decrease in the contractile response to both agonist stimulation and membrane depolarization-dependent contractions and a decrease in Ca(2+)-dependent myosin light chain (MLC) phosphorylation, the primary step in the initiation of smooth muscle contraction. Inhibition of PI3-kinase also depressed phorbol dibutyrate-induced contractions, which are not dependent on either Ca(2+) or MLC phosphorylation but are dependent on protein kinase C. To determine the Ca(2+)-dependent site of action of PI3-kinase, we determined the effect of several inhibitors of calcium metabolism on LY-294002-dependent inhibition of contraction. These inhibitors included nifedipine, SK&F-96365, and caffeine. Only SK&F-96365 blocked the LY-294002-dependent inhibition of contraction. Interestingly, all compounds blocked the LY-294002-dependent inhibition of MLC phosphorylation. Our results suggest that activation of PI3-kinase is involved in a Ca(2+)- and MLC phosphorylation-independent pathway for contraction likely to involve protein kinase C. In addition, our results also suggest that activation of PI3-kinase is involved in Ca(2+)-dependent signaling at the level of receptor-operated calcium channels.     

Properties and reaction with iodoacetamide of adenosine 5′-triphosphate–creatinine phosphotransferase from human skeletal muscle. Further evidence about the role of the essential thiol group in relation to the mechanism of action

1. The purification of creatine kinase from human and monkey skeletal muscle by horizontal electrophoresis on Sephadex blocks is described. 2. The purified enzymes are shown to have similar chemical and kinetic properties to the rabbit muscle enzyme and a common mechanism is inferred. 3. Iodoacetamide has a similar apparent second-order inhibition constant with the human and rabbit enzymes, but the inhibition does not go to completion with the former. This is even more marked with the monkey enzyme, which has more reactive thiol groups, but inhibition is only about 50%. 4. Single substrates have little effect on the inhibition by iodoacetamide, but with the primate enzymes, in contrast with the rabbit enzyme, high concentrations of ADP-Mg(2+) plus creatine convert the essential thiol group from being pH-independent into one with a normal ionization. Low concentrations of ADP-Mg(2+) plus creatine first enhance the rate of inactivation, but cause protection as the reaction proceeds. These results are interpreted to indicate an activation of the thiol group on the subunit to which the substrates bind and a co-operatively induced decrease in the activity of the thiol group on the other subunit which lacks substrates. 5. The effects of a substrate equilibrium mixture on the rate of inhibition are essentially those of ADP-Mg(2+) plus creatine. 6. Since no substrate combination affords significant protection to the thiol group associated with the catalytic site to which the substrates are bound, it is concluded that any mechanism involving the thiol group in a direct participation in the transition-state complex of the catalytic reaction must be abandoned unless the transition state is only a small part of the time taken for one catalytic cycle.