Magnitude Of Protection Research Articles

Distinct interaction modes of an AKAP bound to two regulatory subunit isoforms of protein kinase A revealed by amide hydrogen/deuterium exchange

The structure of an AKAP docked to the dimerization/docking (D/D) domain of the type II (RIIalpha) isoform of protein kinase A (PKA) has been well characterized, but there currently is no detailed structural information of an AKAP docked to the type I (RIalpha) isoform. Dual-specific AKAP2 (D-AKAP2) binds in the nanomolar range to both isoforms and provided us with an opportunity to characterize the isoform-selective nature of AKAP binding using a common docked ligand. Hydrogen/deuterium (H/D) exchange combined with mass spectrometry (DXMS) was used to probe backbone structural changes of an alpha-helical A-kinase binding (AKB) motif from D-AKAP2 docked to both RIalpha and RIIalpha D/D domains. The region of protection upon complex formation and the magnitude of protection from H/D exchange were determined for both interacting partners in each complex. The backbone of the AKB ligand was more protected when bound to RIalpha compared to RIIalpha, suggesting an increased helical stabilization of the docked AKB ligand. This combined with a broader region of backbone protection induced by the AKAP on the docking surface of RIalpha indicated that there were more binding constraints for the AKB ligand when bound to RIalpha. This was in contrast to RIIalpha, which has a preformed, localized binding surface. These distinct modes of AKAP binding may contribute to the more discriminating nature of the RIalpha AKAP-docking surface. DXMS provides valuable structural information for understanding binding specificity in the absence of a high-resolution structure, and can readily be applied to other protein-ligand and protein-protein interactions.

The Repeated Bout Effect In Ipsilateral And Contralateral Limbs After Single Bouts Of Lengthening Contractions

A single bout of lengthening contractions can result in profound adaptations known as the repeated bout effect (RBE), which has been shown to protect skeletal muscle from subsequent insults of lengthening contractions. Chronic eccentric training has been shown to produce neuromuscular adaptations in the untrained homologous muscle, making the expectation tenable that acute bouts of eccentric contractions would evoke rapid adaptation in the contralateral limb. PURPOSE Firstly, to examine whether the RBE exists in the contralateral limb and secondly, to compare any protection to that manifested in the ipsilateral limb. METHODS Sixteen subjects, randomly assigned to an ipsilateral (IL) or contralateral (CL) group, performed maximal lengthening contractions of the elbow flexors, followed by an identical bout carried out on either the CL or IL limb 2 weeks later. Damage markers of creatine kinase (CK), muscle soreness (DOMS) and maximal isometric contraction (MVC) were measured before, 48 h and 96 h after the initial exercise and at the same time periods before and after the subsequent bout. [CK] data were log transformed and MVC was normalised and expressed as a percentage change from baseline. RESULTS: The CL group showed a diminished decrement in MVC and reduced DOMS in bout 2 (F = 9.0, P = 0.020; F = 7.6, P = 0.028, respectively). CK and DOMS showed significant group × bout × time interactions (F = 4.4, P = 0.022; F = 4.0, P = 0.030, respectively). Post-hoc pair-wise analysis revealed that in the second bout, compared to the CL group, the IL group demonstrated reduced CK at 96 h (P <0.001) and less soreness at 48 h (P = 0.006). MVC showed a group × time interaction (F = 5.6, P = 0.009); post-hoc pair-wise comparisons showed the IL group had a lower decrement in torque than the CL group at 48 h (P <0.001) and 96 h (P <0.045) in bout 2. CONCLUSIONS This is the first investigation to demonstrate evidence of a repeated bout effect in the contralateral limb from a single bout of lengthening contractions. However, the magnitude of protection is less in the CL limb than in the IL limb.

Serotype 1 Viruses Modified by Backpassage or Insertional Mutagenesis: Approaching the Threshold of Vaccine Efficacy in Marek's Disease

Improved vaccines to control Marek's disease (MD) in chickens are desired by the poultry industry but have been difficult to develop. Studies were conducted to evaluate strategies for deriving MD vaccines of high protective efficacy, irrespective of virulence. Candidate viruses from parent strains representing v and vv+ pathotypes were modified by cell culture passage, backpassage in chickens, or insertional mutagenesis following cocultivation with retroviruses. Ten strains considered most likely to exhibit high protective efficacy were selected for further study. The ability of these modified viruses to protect commercial or maternal antibody-positive (ab+) chickens against virulent MD virus (MDV) challenge was compared with that of strain CVI988, the standard commercial MD vaccine. Modified strains were also evaluated for the ability to induce lymphomas or other pathologic changes in ab+ and antibody-negative (ab-) chickens. Two of the 10 modified viruses, strains RM1 and CVI988/BP5, provided high levels of protection against highly virulent MDV challenge. The magnitude of protection was greater than that of one laboratory and two commercial preparations of CV1988, but was approximately equal to that of two other commercial preparations of CVI988 in laboratory and field tests. Three of the strains, including RMI and CVI988/BP5, induced lymphoid organ atrophy in ab-chicks but not in ab+ commercial chicks, a property designated here as L phenotype. Seven strains, including two L+ strains, were mildly oncogenic for ab- chicks, a property designated here as O phenotype. Five of these strains caused no tumors in ab+ chickens. The two fully attenuated strains induced neither lymphomas nor lymphoid organ atrophy. The L and O phenotypes appeared not to be linked, and both (especially the L phenotype) appeared associated with high levels of protection. These studies also illustrated differences in the protective efficacy of different preparations of CVI988 vaccine, indicating the need to choose carefully the most protective strains as controls for efficacy studies. A new vv+ strain, designated as 686, is described and appears useful as a challenge virus; it is the most virulent of the 48 field isolates of MDV thus far pathotyped in this laboratory. These findings support the conclusion that new virus strains with high levels of protective immunity comparable to that of CVI988 can be developed. However, the question of whether strains can be developed that exceed the efficacy of current CVI988-based vaccines remains unanswered. After more than 30 years of unsuccessful endeavor by many laboratories toward this goal, it now may be useful to consider whether the efficacy of MD vaccines is limited by some type of biologic threshold.

Resistant Starch and Colorectal Neoplasia

There are several approaches to examining the relationship between resistant starch (RS) and development of colorectal cancer (CRC). These include examination of epidemiological relationships, objective testing of effects of RS given to humans on biological events of relevance to CRC, and studies in animal models where protection and mechanisms of protection can be directly tested. Nine epidemiological studies have examined the relationship between starch and CRC and/or adenomas. Most show a significant protective effect. However, epidemiological tools for measuring consumption of RS are poorly developed and so a benefit for RS can only be inferred. On balance, the magnitude of protection by starch appears to be in the order of 25-50%. Human intervention studies have examined the effect of various types and amounts of RS consumption on colonic biology. To generalize from these studies, RS softens stools and increases stool bulk, decreases pH, increases short-chain fatty acids (SCFAs) including butyrate, reduces products of protein fermentation, and decreases bile salts in fecal water. Such changes seem to be achieved within about 4 weeks of commencing consumption. The greatest effects are seen with the highest doses where increased fecal starch recovery is observed. A modest number of animal studies have been undertaken. Those examining effects of RS on colonic biology and biomarkers for CRC confirm and extend the results in humans. RS modifies the lumenal environment, largely through altered fermentation of polysaccharides and proteins. RS also affects epithelial biology in that it increases apoptotic deletion of genetically damaged cells. More work is needed to define what types and combinations of RS, perhaps with probiotics, exert the greatest effects on colonic environment and epithelial biology, and then to test these in the cancer models for their protective effect. A few studies have examined effect of RS on cancer as an end point in several rodent models, but the results are not clear cut. In conclusion, consumption of RS dramatically affects the colonic lumenal environment and facilitates apoptotic deletion of genetically damaged cells in the colon, several of which are considered to be biomarkers associated with risk for CRC. These effects can be interpreted as reflecting improved colonic health, which might be of benefit in protection against CRC. Direct evidence for protection is still not available.

Treatment of latent tuberculosis infection in HIV infected persons.

Individuals with HIV infection are at an increased risk of developing active tuberculosis. It is known that treatment of latent tuberculosis infection (LTBI), also referred to as preventive therapy or chemoprophylaxis, helps to prevent progression to active disease in human immunodeficiency virus (HIV) negative populations. However, the extent and magnitude of protection (if any) associated with preventive therapy in those infected with HIV should be quantified. To determine the effectiveness of tuberculosis preventive therapy in reducing the risk of active tuberculosis and death in persons infected with HIV. We searched the Cochrane Controlled Trials Register (CCTR), MEDLINE, EMBASE, AIDSLINE, AIDSTRIALS and AIDSDRUGS. We also scanned reference lists of articles and contacted authors and other researchers in the field. We included studies in which HIV positive individuals were randomly allocated to preventive therapy for TB and placebo, or to alternative TB preventive therapy regimens. Participants could be tuberculin skin test positive or negative, but without active tuberculosis. Two reviewers independently applied study selection criteria, assessed study quality and extracted data. Effects were assessed using relative risk for dichotomous data and weighted mean difference for continuous data. 11 trials were included with a total of 8,130 randomized participants. Preventive therapy (any anti-TB drug) versus placebo was associated with a lower incidence of active tuberculosis (RR 0.64, 95% CI 0.51 to 0.81). This benefit was more pronounced in individuals with a positive tuberculin skin test (RR 0.38, 95% CI 0.25 to 0.57) than in those who had a negative test (RR 0.83, 95% CI 0.58 to 1.18.). Limited data suggest that the initial protective effect against tuberculosis may decline over the short to medium term. Efficacy was similar for all regimens (regardless of drug type, frequency or duration of treatment). However, compared to INH monotherapy, short -course multi-drug regimens were much more likely to require discontinuation of treatment due to adverse effects. Overall, there was no evidence that preventive therapy versus placebo reduced all-cause mortality (RR 0.95, 95% CI 0.85 to 1.06), although a favourable trend was found in people with a positive tuberculin test (RR 0.80, 95% CI 0.63 to 1.02). Treatment of latent tuberculosis infection (LTBI) reduces the risk of active tuberculosis in HIV positive individuals with a positive tuberculin skin test. The choice of regimen will depend on factors such as cost, adverse effects, adherence and drug resistance. Future studies should assess these aspects. In addition, trials evaluating the long-term effects of anti-tuberculosis chemoprophylaxis and the influence of level of immunocompromise on effectiveness are needed.

Hypothermic preconditioning induces rapid tolerance to focal ischemic injury in the rat

Stressful, preconditioning stimuli can elicit rapid and delayed forms of tolerance to ischemic injury. The identification and characterization of preconditioning stimuli that are effective, but relatively benign, could enhance the clinical applicability of induced tolerance. This study examines the efficacy of brief hypothermia as a preconditioning stimulus for inducing rapid tolerance. Rats were administered hypothermic preconditioning or sham preconditioning and after an interval of 20–120 min were subjected to transient focal ischemia using a three-vessel occlusion model. The volume of cerebral infarction was measured 24 h or 7 days after ischemia. In other experiments, the depth or duration of the hypothermic stimulus was manipulated, or a protein synthesis inhibitor (anisomycin) was administered. Twenty minutes of hypothermia delivered 20 or 60 (but not 120) min prior to ischemia significantly reduces cerebral infarction. The magnitude of protection is enhanced with deeper levels of hypothermia, but is not affected by increasing the duration of the hypothermic stimulus. Treatment with a protein synthesis inhibitor does not block the induction of rapid tolerance. Hypothermic preconditioning elicits a rapid form of tolerance to focal ischemic injury. Unlike delayed tolerance induced by hypothermia, rapid tolerance is not dependent on either de novo protein synthesis or the duration of the preconditioning stimulus. These findings suggest that the mechanisms underlying rapid and delayed tolerance induced by hypothermia differ fundamentally. Brief hypothermia could provide a rapid means of inducing transient tissue protection in the context of predictable ischemic events.

Reproductive factors and familial predisposition for breast cancer by age 50 years. A case-control-family study for assessing main effects and possible gene-environment interaction.

The effect of environmental/lifestyle factors on breast cancer risk may be modified by genetic predisposition. In a population-based case-control-family study performed in Germany including 706 cases by age 50 years, 1381 population, and 252 sister controls, we investigated main effects for environmental/lifestyle factors and genetic susceptibility and gene-environment interaction (G x E). Different surrogate measures for genetic predisposition using pedigree information were used: first-degree family history of breast or ovarian cancer; and gene carrier probability using a genetic model based on rare dominant genes. Possible G x E interaction was studied by (1) logistic regression using cases and population controls including an interaction term; (2) comparing results using sister controls and population controls; (3) case-only analysis with logistic regression and (4) a mixture logistic model. Familial predisposition showed the strongest main effect and the estimated gene carrier probability gave the best fit. High parity and longer duration of breastfeeding reduced breast cancer risk significantly, a history of abortions increased risk and age at menarche showed no significant effect. We found significant G x E interaction between parity and genetic susceptibility using different surrogate measures. In women most likely to have a high genetic susceptibility, high parity was less protective. Later age at menarche was protective in women with a positive family history. No evidence for G x E interaction was found for breastfeeding and abortion. These findings corroborate results from other studies and provide further evidence that the magnitude of protection from parity is reduced in women most likely to have a genetic risk in spite of the limitations of using surrogate genetic measures.

Vascular endothelial growth factor protects cultured rat hippocampal neurons against hypoxic injury via an antiexcitotoxic, caspase-independent mechanism.

The authors investigated the effect of vascular endothelial growth factor (VEGF) on hypoxic injury of cultured rat hippocampal neurons. Treatment with glutamate receptor antagonists prevented hypoxic neuron death. The same magnitude of protection was observed in cultures treated with VEGF, which also reduced excitotoxic neuron death induced directly by an exposure to -methyl-d-aspartate. Vascular endothelial growth factor did not alter the activation of the transcription factor nuclear factor-kappaB during hypoxia and protected cells in a PI-3-kinase-independent manner. Vascular endothelial growth factor failed to protect against staurosporine-induced, caspase-dependent apoptosis. These data suggest that VEGF-induced protection against hypoxic injury primarily involves the inhibition of excitotoxic processes.

Powerful and prolonged protection of human retinal pigment epithelial cells, keratinocytes, and mouse leukemia cells against oxidative damage: the indirect antioxidant effects of sulforaphane.

Mammalian cells are equipped with elaborate systems for protection against the toxicity of reactive oxygen and nitrogen species and electrophiles that are constant dangers to the integrity of their DNA. Phase 2 enzymes (e.g., glutathione transferases, NAD(P)H:quinone reductase) and glutathione synthesis are widely recognized as playing major protective roles against electrophilic carcinogens, but their antioxidant functions have attracted far less attention. The cytotoxicities of four oxidative stressors (menadione, tert-butyl hydroperoxide, 4-hydroxynonenal, and peroxynitrite) for human adult retinal pigment epithelial cells (ARPE-19) were quantified by measuring the concentration dependence of cell death and were expressed as the median effect dose (D(m)) for each oxidant. After treatment of ARPE-19 cells for 24 h with 0-5 microM concentrations of sulforaphane (the powerful Phase 2 enzyme inducer isolated from broccoli), the toxicities of the oxidants were markedly reduced as shown by 1.5- to 3-fold increases in D(m) values. The magnitude of protection was a function of the nature of the oxidants and the concentrations of both the oxidants and sulforaphane. Protection was prolonged and persisted for several days after removal of sulforaphane before returning to control levels. The sulforaphane-dependent increases in specific activities of cytosolic quinone reductase and the glutathione levels were highly significantly correlated with the degree of protection as measured by D(m) values. Antioxidant protection was also demonstrated for human HaCaT keratinocytes and L1210 murine leukemia cells. It is therefore highly likely that the multifaceted and prolonged antioxidant protection provided by sulforaphane is a general phenomenon that is mediated through induction of the Phase 2 enzyme response.

Low- and High-Dose Pills are Equally Protective against Ovarian Cancer

This article discusses two separate population-based case-control studies on the protective function of low- and high-dose oral contraceptives (OCs) against ovarian cancer. Overall the ovarian cancer study found that women who have ever used the common types of OCs which contain low doses of estrogen and progestin are 50% less likely than never-users of the pill to develop ovarian cancer. In addition it was found that this level of protection is identical to that afforded by older OCs with higher hormone doses. These findings suggest that the ability of the OCs to prevent ovarian cancer has been unaffected by changes made in the pill formulations to make the method safer. Similarly evidence from the benign ovarian tumor study suggests that ever-use of OCs reduces the odds of non-cancerous ovarian tumors by 20% and the decrease in risk is independent of estrogen dose. In both studies the magnitude of protection increased with longer durations of pill use.

Helium-neon laser preirradiation induces protection against UVC radiation in wild-type E. coli strain K12AB1157.

We have observed that preirradiation with a helium-neon laser (632.8 nm) induces protection against UVC radiation in wild-type E. coli strain K12AB1157. The magnitude of protection was found to depend on the helium-neon laser irradiance, exposure time, and period of incubation between helium-neon laser exposure and subsequent UVC irradiation. The optimum values for dose, irradiance and interval between the two exposures were found to be 7 kJ/m(2), 100 W/m(2) and 1 h, respectively. The possible involvement of singlet oxygen in the helium-neon laser-induced protection is also discussed.

The role of T-cell phenotyping during immunosuppression withdrawal in liver transplantation

time of fas-antibody, 3 hours prior to the antibody, or 1 hour postantibody administration. A single dose of 10 mg/kg at the time of fasantibody administration provides complete protection when liver function is measured at 1 day and 7 days. There is good correspondence between serum transaminase levels and the extent of apoptosis observed histologically. There is also a good correlation between the magnitude of protection and the inhibition of caspase activity, measured either by substrate cleavage activity, Western blot, or immunocytochemistry. The therapeutic potential of caspase inhibitors in ameliorating fas or cytokine induced hepatocelluar injury appears promising and is the subject of further investigation.

Flavonoids as inhibitors or enhancers of the cytotoxicity of tumor necrosis factor-alpha in L-929 tumor cells.

The effects of some selected flavonoids on tumor necrosis factor-alpha (TNF)-induced cytotoxicity in murine fibroblast L-929 cells were studied. All of the flavanones tested as well as a flavan, epicatechin, protected L-929 cells from TNF-induced cell death of the flavanones tested, hesperetin, isosakuranetin, and pinocembrin failed to modify TNF cytotoxicity, but the 3',4'-dihydroxyflavanones, eriodictyol and taxifolin, showed a protective effect. Eriodictyol was the most potent protective agent of all the flavonoids tested, while a 4'-hydroxyflavanone, naringenin, rather showed enhancement of TNF cytotoxicity. Of the flavones tested, chrysin and apigenin markedly augmented the cytotoxicity of TNF, while luteolin showed a weak protective effect. The magnitude of protection and potentiation by these flavonoids were concentration-dependent and these effects were not altered when the flavonoids were added as much as 2 h after TNF treatment.

Limitation of infarct size by myocardial ischemic preconditioning.

Myocardial ischemic preconditioning (IP) has caught the attention and imagination of researchers throughout the world (7). And for good reason: the magnitude of protection against ischemic injury conferred by IP is tremendous, far surpassing that offered by past pharmacological therapies. Although the original description of IP focused on limitation of myocardial infarction following acute coronary occlusion and reperfusion, IP may also decrease the incidence of ischemia-induced arrhythmias and improve post-ischemic cardiac function. However, in this article the discussion will be confined to the infarctlimiting effect of IP. Upon suffering a brief episode of ischemia, the myocardium instigates some change in itself which protects it from subsequent ischemic events. On an organ level the visible end-point is a decrease in infarct. This grossly visible change is the result of the cellular transduction of a signal and the institution of an adaptive cellular modification. But what precisely is that cellular process?

Myocardial Ischemic Preconditioning

Protection of ischemic myocardium through transient antecedent sublethal ischemia (myocardial ischemic preconditioning, IP) is a well established laboratory phenomenon which has caught the attention and imagination of clinicians and researchers throughout the world. The magnitude of protection against ischemic injury conferred by IP is tremendous, far surpassing that offered by past pharmacological therapies. Indirect evidence suggests that IP occurs in human hearts as well. But whether IP is a naturally occurring phenomenon in humans, or is relevant to the practice of clinical medicine, remains unclear.

Neuroprotective effect of 5-HT 3 receptor antagonist on ischemia-induced decrease in CA1 field potential in rat hippocampal slices

The effect of 5-HT 3 receptor agonists and antagonists on the hypoxia/hypoglycemia (ischemia)-induced decrease in CA1 field potential elicited by stimulation of Schaffer collaterals was investigated using rat hippocampal slices. Treatment with the 5-HT 3 receptor agonist, 2-methyl-5-HT (1–10 μM), exaceebated the ischemia-induced decreased in CA1 field potential, whereas treatment with the 5-HT 3 receptor antagonist. Y-25130 (0.1–100 μM), or the 5-HT 2 receptor antagonist, ketanserin (10, 100 μM), produced dose-dependent neuroprotection against the ischemia-induced decrease. However, in normal non-ischemic solution these treatments did not significantly change the CA1 field potential. The protective action of Y-25130 was blocked by co-treatment with 2-methyl-5-HT. The magnitude of protection in the Y-25130-treated group (EC 50, 1.8 μM) was about 20 times greater than that in the ketanserin-treated group (EC 50, 33 μM). The present study demonstrated that stimulation of 5-HT 3 receptors plays a detrimental role in the development of ischemic damage, whereas blockade of the 5-HT 3 receptor plays a neuroprotective role in ischemic damage, suggesting a facilitatory role of 5-HT neurons in ischemia-induced neuronal deficits.

Captopril: a protective agent in renal warm ischemia in rats.

Captopril, an angiotensin-converting enzyme inhibitor, was used as a protective agent before and after 90 min of renal warm ischemia in rats. At a dose of 1 mg/kg, it was able to lower the postoperative serum creatinine values significantly (from 6.3 to 2.5 mg% on the 2nd postoperative day) in unilaterally nephrectomized animals. Increasing the dose to 4 and 8 mg/kg or combining captopril with hypertonic mannitol (10 ml/kg of a 15% aqueous solution) did not improve these figures significantly. The same magnitude of protection was obtained when captopril was given either before or just after the ischemia. In terms of mortality the differences among unprotected and protected groups were very important: only 6 of 24 unprotected animals survived the 5th postoperative day while 42 of 44 protected animals survived.

Protection by ascorbate against acetylphenylhydrazine induced Heinz body formation in normal human and sheep erythrocytes

Abstract Ascorbate was found to siqnificantly (P < 0.05) reduce the occurrence of heinz body formation in normal human and sheep red cells incubated with acetylphenylhydrazine. While in fundamental agreement with earlier findings of Winterbourn1 with glucose‐6‐phosphate dehydrogenase (G‐6‐PD) deficient human red cells, in the present study the concentrations at which ascorbate initiated significant protection in both sheep and normal humans were considerably higher than in the Winter‐bourn1 study and the magnitude of protection, while statistically significant (P < 0.05), was considerably less than reported by Winterbourn.1

Enzymatic measurement of the radioprotective activity of chemical agents

Modification of radiation-induced changes in the adenosinetriphosphatase activity of the spleens and cholinesterase activity of the small intestine of rats was employed as a means of quantitating the protection by chemical agents against radiation damage to these tissues. The magnitude of protection was expressed as per cent reduction of the biologically effective radiation dose and was calculated from radiation dose-response curves. Hydroxylamine (75 mg/kg), cysteine (1000 mg/kg), and glutathione (900 mg/kg) caused substantial reductions in the biologically effective dose of radiation in the spleen and intestine when given prior to X-ray. Survival studies indicated that these compounds all provide a similar amount of protection. Combinations of hydroxylamine with cysteine, glutathione, or AET were mcre effective in preventing radiation-induced mortality than any of the compounds given alone. The results of this study demonstrated the usefulness of enzyme assays for evaluating the efficacy of chemical agents in protecting tissues from radiation damage. The findings also suggest the possible value of a similar procedure in searching for antidotes for toxic chemical agents.