Caffeine prevents protection in two human models of ischemic preconditioning

Radionuclide imaging of apoptosis for clinical application

Apoptosis was a natural, non-inflammatory, energy-dependent form of programmed cell death (PCD) that can be discovered in a variety of physiological and pathological processes. Based on its characteristic biochemical changes, a great number of apoptosis probes for single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have been developed. Radionuclide imaging with these tracers were potential for the repetitive and selective detection of apoptotic cell death in vivo, without the need for invasive biopsy. In this review, we overviewed molecular mechanism and specific biochemical changes in apoptotic cells and summarized the existing tracers that have been used in clinical trials as well as their potentialities and limitations. Particularly, we highlighted the clinic applications of apoptosis imaging as diagnostic markers, early-response indicators, and prognostic predictors in multiple disease fields.

Targeting phosphatidylserine for radionuclide-based molecular imaging of apoptosis

One major characteristic of programmed cell death (apoptosis) results in the increased expression of phosphatidylserine (PS) on the outer membrane of dying cells. Consequently, PS represents an excellent target for non-invasive imaging of apoptosis by single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Annexin V is a 36 kDa protein which binds with high affinity to PS in the presence of Ca²⁺ ions. This makes radiolabeled annexins valuable apoptosis imaging agents for clinical and biomedical research applications for monitoring apoptosis in vivo. However, the use of radiolabeled annexin V for in vivo imaging of cell death has been met with a variety of challenges which have prevented its translation into the clinic. These difficulties include: complicated and time-consuming radiolabeling procedures, sub-optimal biodistribution, inadequate pharmacokinetics leading to poor tumour-to-blood contrast ratios, reliance upon Ca²⁺ concentrations in vivo, low tumor tissue penetration, and an incomplete understanding of what constitutes the best imaging protocol following induction of apoptosis. Therefore, new concepts and improved strategies for the development of PS-binding radiotracers are needed. Radiolabeled PS-binding peptides and various Zn(II) complexes as phosphate chemosensors offer an innovative strategy for radionuclide-based molecular imaging of apoptosis with PET and SPECT. Radiolabeled peptides and Zn(II) complexes provide several advantages over annexin V including better pharmacokinetics due to their smaller size, better availability, simpler synthesis and radiolabeling strategies as well as facilitated tissue penetration due to their smaller size and faster blood clearance profile allowing for optimized image contrast. In addition, peptides can be structurally modified to improve metabolic stability along with other pharmacokinetic and pharmacodynamic properties. The present review will summarize the current status of radiolabeled annexins, peptides and Zn(II) complexes developed as radiotracers for imaging apoptosis through targeting PS utilizing PET and SPECT imaging.

Association between lifetime coffee consumption and late life cerebral white matter hyperintensities in cognitively normal elderly individuals

Coffee consumption is associated with cerebral hypoperfusion that may contribute to the development of cerebral white matter hyperintensities (WMH). We investigated the effect of lifetime coffee consumption on the volume of WMH (V_WMH) in late life, and compared the effect between men and women since caffeine clearance may be different between sexes. We enrolled 492 community-dwelling cognitively normal elderly individuals (73.4 ± 6.7 years old on average) from the Korean Longitudinal Study on Cognitive Aging and Dementia. We evaluated their patterns and amounts of coffee consumption using a study-specific standardized interview and estimated cerebral V_WMH by automatic segmentation of brain fluid-attenuated inversion recovery sequence magnetic resonance images. Higher cumulative lifetime coffee consumption was associated with higher logV_WMH in both sexes (p = 0.030). The participants who consumed more than 2 cups of coffee per day on average in their lifetime showed higher logV_WMH in late life than those who consumed less. When both sexes were analyzed separately, these coffee-logV_WMH associations were found only in women, although the volumes of brain and white matter of women were smaller than those of men. Our findings suggest that prolonged high coffee consumption may be associated with the risk of WMH in late life.

Plasma levels of the cardiovascular protective endogenous nucleoside adenosine are reduced in patients with primary aldosteronism without affecting ischaemia-reperfusion injury: A prospective case-control study

BACKGROUND

Patients with primary aldosteronism (PA) experience more cardiovascular events compared to patients with essential hypertension (EHT), independent from blood pressure levels. In animals, mineralocorticoid receptor antagonists limit ischaemia-reperfusion (IR) injury by increasing extracellular adenosine formation and adenosine receptor stimulation. Adenosine is an endogenous compound with profound cardiovascular protective effects. Firstly, we hypothesized that patients with PA have lower circulating adenosine levels which might contribute to the observed increased cardiovascular risk. Secondly, we hypothesized that by this mechanism, patients with PA are more susceptible to IR compared to patients with EHT.

DESIGN

In our prospective study in 20 patients with PA and 20 patients with EHT, circulating adenosine was measured using a pharmacological blocker solution that halts adenosine metabolism after blood drawing. Brachial artery flow-mediated dilation (FMD) before and after forearm IR was used as a well-established method to study IR injury.

RESULTS

Patients with PA had a 33% lower adenosine level compared to patients with EHT (15.3 [13.3-20.4] vs 22.7 [19.4-36.8] nmol/L, respectively, P < .01). The reduction in FMD after IR, however, did not differ between patients with PA and patients with EHT (-1.0 ± 2.9% vs -1.6 ± 1.6%, respectively, P = .52).

CONCLUSIONS

As adenosine receptor stimulation induces various powerful protective cardiovascular effects, its lower concentration in patients with PA might be an important novel mechanism that contributes to their increased cardiovascular risk. We suggest that modulation of the adenosine metabolism is an exciting novel pharmacological opportunity to limit cardiovascular risk in patients with PA that needs further exploration.

Remote ischaemic preconditioning does not modulate the systemic inflammatory response or renal tubular stress biomarkers after endotoxaemia in healthy human volunteers: a single-centre, mechanistic, randomised controlled trial

BACKGROUND

Remote ischaemic preconditioning (RIPC) consists of repeated cycles of limb ischaemia and reperfusion, which may reduce perioperative myocardial ischaemic damage and kidney injury. We hypothesised that RIPC may be beneficial by attenuating the systemic inflammatory response. We investigated whether RIPC affects the response in humans to bacterial endotoxin (lipopolysaccharide [LPS]) by measuring plasma cytokines and renal cell-cycle arrest mediators, which reflect renal tubular stress.

METHODS

Healthy male volunteers were randomised to receive either daily RIPC for 6 consecutive days (RIPC_multiple, n=10) plus RIPC during the 40 min preceding i.v. LPS (2 ng kg^-1), RIPC only during the 40 min before LPS (RIPC_single, n=10), or no RIPC preceding LPS (control, n=10). As a surrogate marker of renal tubular stress, the product of urinary concentrations of two cell-cycle arrest markers was calculated (tissue inhibitor of metalloproteinases-2 [TIMP2]*insulin-like growth factor binding protein-7 [IGFBP7]). Data are presented as median (inter-quartile range).

RESULTS

In both RIPC groups, RIPC alone increased [TIMP2]*[IGFBP7]. LPS administration resulted in fever, flu-like symptoms, and haemodynamic alterations. Plasma cytokine concentrations increased profoundly during endotoxaemia (control group: tumor necrosis factor alpha [TNF-α] from 14 [9-16] pg ml^-1 at baseline to 480 [284-709] pg ml^-1 at 1.5 h after LPS; interleukin-6 [IL-6] from 4 [4-4] pg ml^-1 at baseline to 659 [505-1018] pg ml^-1 at 2 h after LPS). LPS administration also increased urinary [TIMP2[*[IGFBP7]. RIPC had no effect on LPS-induced cytokine release or [TIMP2]*[IGFBP7].

CONCLUSIONS

RIPC neither modulated systemic cytokine release nor attenuated inflammation-induced tubular stress after LPS. However, RIPC alone induced renal markers of cell-cycle arrest.

CLINICAL TRIAL REGISTRATION

NCT02602977.

Impact of 8 weeks of repeated ischemic preconditioning on running performance

PURPOSE

To examine if repeated exposure to IPC treatment prior to training sessions improves oxygen uptake and 1-km running performance in highly trained middle-distance runners.

METHODS

Fourteen highly trained endurance runners (11 male/3 female, 19 ± 2 years, 64 ± 5 ml kg^-1 min^-1) completed a baseline maximal oxygen consumption ([Formula: see text]) test and 1-km running performance test before random assignment to an IPC or control group. Both groups were prescribed identical endurance training over an 8-week varsity season; however, the IPC group performed an IPC protocol (5 min ischemia, repeated 3 times, each separated by 5 min reperfusion) before every training session. After 8 weeks of training, participants completed a follow-up [Formula: see text] test and 1-km time trial.

RESULTS

[Formula: see text] did not increase from baseline in either group following the 8-week training bout (P = 0.2), and neither group varied more than the other ([Formula: see text] = IPC 0.6 ± 2 ml kg^-1 min^-1; control 1.5 ± 2 ml kg^-1 min^-1, P = 0.6) or beyond typical measurement error. The IPC decreased 1-km time trial time by 0.4% (0.5 ± 2 s), while the control group decreased by 1% (1.5 ± 3 s), but neither change was significant compared to baseline (P = 0.2). There was also no difference in time trial improvement between IPC and control (P = 0.6). However, there was a trend towards IPC significantly improving running economy at low intensity (P = 0.057).

CONCLUSION

Our data suggest that over a normal 8-week season in a population of highly trained middle-distance runners there is no benefit of undergoing chronic, repeated IPC treatments before training for augmenting maximal aerobic power or 1-km performance time.

Adenosine Receptor Activation in the "Trigger" Limb of Remote Pre-Conditioning Mediates Human Endothelial Conditioning and Release of Circulating Cardioprotective Factor(s)

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Pre-conditioning has emerged as a potentially powerful means of reducing ischemia-reperfusion injury.

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Several animal models have implicated adenosine in pre-conditioning pathways, but its role in human physiology is unknown.

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In human volunteers, the authors demonstrate that adenosine receptor activation in “trigger” tissue is an important step in initiating a pre-conditioning signal, but adenosine receptor blockade in “target” tissue does not block the protection afforded by pre-conditioning.

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The authors also demonstrate that pre-conditioning elaborates a transferrable cardioprotective factor(s) into the serum. This elaboration is prevented by adenosine receptor blockade but can be mirrored by the infusion of exogenous adenosine.

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An improved understanding of the physiological effectors of pre-conditioning may allow for better targeted clinical studies of pre-conditioning and pre-conditioning mimetics in the future.

Remote ischemic pre-conditioning (rIPC) has emerged as a potential mechanism to reduce ischemia-reperfusion injury. Clinical data, however, have been mixed, and its physiological basis remains unclear, although it appears to involve release of circulating factor(s) and/or neural pathways. Here, the authors demonstrate that adenosine receptor activation is an important step in initiating human pre-conditioning; that pre-conditioning liberates circulating cardioprotective factor(s); and that exogenous adenosine infusion is able to recapitulate release of this factor. However, blockade of adenosine receptors in ischemic tissue does not block the protection afforded by pre-conditioning. These data have important implications for defining the physiology of human pre-conditioning and its translation to future clinical trials.

Caffeine Improves Heart Rate Without Improving Sepsis Survival

INTRODUCTION

Caffeine is consumed on a daily basis for its nervous system stimulant properties and is a global adenosine receptor antagonist. Because adenosine receptors have been found to play a major role in regulating the immune response to a septic insult, we investigated if caffeine consumption prior to a septic insult would alter immunological and physiological responses, as well as survival.

METHODS

Two separate experimental designs were used, both using outbred female ICR mice. In the first experiment, mice were administered 20 mg/kg of caffeine (equal to 2-3 cups of coffee for a human) or normal saline intraperitoneally at the time of cecal ligation and puncture (CLP). Immunological parameters including cytokines and local cell recruitment were measured. In the second experiment, caffeine (10 mg/kg per hour) was delivered continuously for 24 h via a subcutaneous infusion pump placed the day prior to CLP, and hemodynamic parameters were examined. In both experiments, survival was followed for 5 days.

RESULTS

A single dose of caffeine at the initiation of sepsis did not alter survival. This single dose of caffeine did significantly increase in plasma levels of the chemokine KC 6 h after the onset of sepsis compared with septic mice given normal saline. There were no changes in interleukin 6 (IL-6) or IL-10 levels in the caffeine groups. Peritoneal lavages performed 24 h after CLP showed no difference in the levels of IL-6, tumor necrosis factor, KC, macrophage inflammatory protein 1, IL-10, or the IL-1 receptor antagonist between caffeine- and normal saline-treated mice. In addition, the lavages yielded similar numbers of cells (4.1 × 10 vehicle vs. 6.9 × 10 caffeine) and bacterial colony-forming units (CFUs, 4.1 million CFUs vehicle vs. 2.8 million CFUs caffeine). In the infusion group, caffeine also did not alter survival. However, caffeine infusion did increase the heart rate prior to CLP and prevented the decline in heart rate after CLP.

CONCLUSION

Caffeine increased the heart rate in mice but does not impact cytokine responses or survival during the acute phase of a polymicrobial sepsis challenge. These data indicate that patients consuming caffeine will not be at risk for increased sepsis mortality.

Exercise-induced ischemic preconditioning and the potential application to cardiac rehabilitation: a systematic review

Exercise-induced ischemic preconditioning (IPC) can be assessed by the results of the second of sequential exercise tests. Exercise-induced IPC is quantified by using the time to 1-mm ST-segment depression, the rate-pressure product at 1-mm ST-segment depression, the maximal ST-segment depression, and the rate-pressure product at the peak of exercise. Few studies reported whether exercise-induced IPC could be used in cardiovascular rehabilitation. A systematic review of the literature limited to human studies was performed using electronic databases, and the main key words were ischemic preconditioning, warm-up phenomenon, and exercise. After careful review, 38 articles were included in the systematic review. This review summarizes the molecular pathways of IPC and describes the first window of protection induced by sequential exercise tests, as well as the effect of medication on exercise-induced IPC. A section on the exercise protocol, mode of exercise, and intensity provides understanding as to what is needed for clinicians to induce IPC with sequential stress tests. The final section of the review is a discussion of the potential use of exercise-induced IPC in a cardiovascular rehabilitation setting. Even if exercise-induced IPC is a well-documented phenomenon, additional studies are needed in order to more fully understand its use in rehabilitation.

Effect of dipyridamole on myocardial reperfusion injury: A double-blind randomized controlled trial in patients undergoing elective coronary artery bypass surgery

Dipyridamole reduces reperfusion-injury in preclinical trials and may be beneficial in patients undergoing coronary angioplasty, but its effect on patients undergoing coronary artery bypass grafting (CABG) is unknown. We hypothesized that dipyridamole limits myocardial reperfusion-injury in patients undergoing CABG. The trial design was a double-blind trial randomizing between pretreatment with dipyridamole or placebo. In all, 94 patients undergoing elective on-pump CABG were recruited between February 2010 and June 2012. The primary endpoint was plasma high-sensitive (hs-) troponin-I at 6, 12, and 24 hours after reperfusion. Secondary endpoints were the occurrence of bleeding, arrhythmias, need for inotropic support, and intensive care unit length of stay. Finally, 79 patients (33 dipyridamole) were included in the per-protocol analysis. Dipyridamole did not significantly affect postoperative hs-troponin-I (change in plasma hs-troponin I -3% [95% confidence interval -23% to 36%]; P > 0.1). Secondary endpoints did not differ between groups. Dipyridamole prior to CABG does not significantly reduce postoperative hs-troponin release.

Cardiovascular effects of long-term caffeine administration in aged rats

AIM

To evaluate the possible beneficial effect of long-term caffeine administration on cardiovascular system in aged rats.

METHODS

This study was carried out on 20 senile male albino rats, aged 18-20 months. Rats were divided into caffeine-treated group, which received 25 mg/kg caffeine by gavage daily for 6 weeks, and control group. All rats were subjected to the following in vivo measurements: body weight, arterial blood pressure, heart rate and ECG recording. In vitro measurements included studying isolated hearts in a Langendorff apparatus for their intrinsic properties as well as plasma levels of lipids, malondialdehyde and nitrate.

RESULTS

Caffeine administration to aged rats significantly enhanced the baseline and maximum values achieved in response to isoproterenol infusion in isolated heart preparation for both maximum rate of tension development (dT/dt max) and time to peak tension (TPT). The responses of hearts isolated from caffeine group to the three doses of isoproterenol infusion also showed a significantly higher dT/dt max with shorter TPT and half relaxation time (1/2 RT) compared to controls. Plasma nitrate was significantly increased and ECG recording was nonsignificantly affected in caffeine group. The plasma levels of total cholesterol, LDL cholesterol as well as in vivo heart rate and systolic, diastolic and mean arterial blood pressures were all significantly increased associated with a significant decrease in HDL cholesterol in caffeine group.

CONCLUSION

Long-term caffeine administration in aged rats increased cardiac inotropy, lusitropy and preserved NO level, which points to a promising potential favorable effect on cardiac intrinsic properties.

A3 Adenosine receptors mediate oligodendrocyte death and ischemic damage to optic nerve

Adenosine receptor activation is involved in myelination and in apoptotic pathways linked to neurodegenerative diseases. In this study, we investigated the effects of adenosine receptor activation in the viability of oligodendrocytes of the rat optic nerve. Selective activation of A3 receptors in pure cultures of oligodendrocytes caused concentration-dependent apoptotic and necrotic death which was preceded by oxidative stress and mitochondrial membrane depolarization. Oligodendrocyte apoptosis induced by A3 receptor activation was caspase-dependent and caspase-independent. In addition to dissociated cultures, incubation of optic nerves ex vivo with adenosine and the A3 receptor agonist 2-CI-IB-MECA(1-[2-Chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-b-D-ribofuranuronamide)-induced caspase-3 activation, oligodendrocyte damage, and myelin loss, effects which were prevented by the presence of caffeine and the A3 receptor antagonist MRS 1220 (N-[9-Chloro-2-(2-furanyl)[1,2,4]-triazolo [1,5-c]quinazolin-5-yl]benzene acetamide). Finally, ischemia-induced injury and functional loss to the optic nerve was attenuated by blocking A3 receptors. Together, these results indicate that adenosine may trigger oligodendrocyte death via activation of A3 receptors and suggest that this mechanism contributes to optic nerve and white matter ischemic damage.

Effect of black tea consumption on brachial artery flow-mediated dilation and ischaemia-reperfusion in humans

Tea consumption is associated with reduced cardiovascular risk. Previous studies found that tea flavonoids work through direct effects on the vasculature, leading to dose-dependent improvements in endothelial function. Cardioprotective effects of regular tea consumption may relate to the prevention of endothelial ischaemia-reperfusion (IR) injury. Therefore, we examined the effect of black tea consumption on endothelial function and the ability of tea to prevent IR injury. In a randomized, crossover study, 20 healthy subjects underwent 7 days of tea consumption (3 cups per day) or abstinence from tea. We examined brachial artery (BA) endothelial function via flow-mediated dilation (FMD), using high resolution echo-Doppler, before and 90 min after tea or hot water consumption. Subsequently, we followed a 20-min ischaemia and 20-min reperfusion protocol of the BA after which we measured FMD to examine the potential of tea consumption to protect against IR injury. Tea consumption resulted in an immediate increase in FMD% (pre-consumption: 5.8 ± 2.5; post-consumption: 7.2 ± 3.2; p < 0.01), whilst no such change occurred after ingestion of hot water. The IR protocol resulted in a significant decrease in FMD (p < 0.005), which was also present after tea consumption (p < 0.001). This decline was accompanied by an increase in the post-IR baseline diameter. In conclusion, these data indicate that tea ingestion improves BA FMD. However, the impact of the IR protocol on FMD was not influenced by tea consumption. Therefore, the cardioprotective association of tea ingestion relates to a direct effect of tea on the endothelium in humans in vivo.

Influence of chronic caffeine on MDMA-induced behavioral and neuroinflammatory response in mice

RATIONALE

Previous research suggests that chronic daily caffeine administration protects against brain injury in different animal models of neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases, ischemic and traumatic brain injury, and allergic encephalitis. However, little is known about the effects of chronic caffeine administration on 3,4-methylenedioxymethamphetamine (MDMA)-induced neuroinflammation.

OBJECTIVE

The present study examines whether chronic caffeine (10, 20, or 30 mg/kg, i.p, for 21 consecutive days) protects against MDMA-induced astrocytic and microglial activation in mice striatum, impairing its neuroinflammatory effects. Additionally, locomotor activity, sensoriomotor reflexes, body temperature, and anxiety were evaluated after caffeine injection on days 0 (basal), 7, 14, and 21 of the chronic treatment in order to assess possible behavioral alterations due to caffeine administration.

METHODS

On day 22, mice pretreated with caffeine or saline received a neurotoxic regimen of MDMA (3 × 20 mg/kg, i.p., 2-h interval) or saline, and changes in body temperature were evaluated. Forty-eight hours after last MDMA or saline injection (day 24), the aforementioned behavioral parameters were investigated and microglia and astroglia activation to MDMA treatment was examined in the mouse striatum.

RESULTS

Caffeine (10 mg/kg) chronically administered completely prevented MDMA-induced glial activation without inducing physiological or behavioral alterations in any of the assays performed.

CONCLUSION

Chronic caffeine consumption at low doses exerts anti-inflammatory effects and prevents MDMA-induced neuroinflammation.

Impact of O-GlcNAc on cardioprotection by remote ischaemic preconditioning in non-diabetic and diabetic patients

AIMS

Post-translational modification of proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) is cardioprotective but its role in cardioprotection by remote ischaemic preconditioning (rIPC) and the reduced efficacy of rIPC in type 2 diabetes mellitus is unknown. In this study we achieved mechanistic insight into the remote stimulus mediating and the target organ response eliciting the cardioprotective effect by rIPC in non-diabetic and diabetic myocardium and the influence of O-GlcNAcylation.

METHODS AND RESULTS

The cardioprotective capacity and the influence on myocardial O-GlcNAc levels of plasma dialysate from eight healthy volunteers and eight type 2 diabetic patients drawn before and after subjection to an rIPC stimulus were tested on human isolated atrial trabeculae subjected to ischaemia/reperfusion injury. Dialysate from healthy volunteers exposed to rIPC improved post-ischaemic haemodynamic recovery (40 ± 6 vs. 16 ± 2%; P < 0.01) and increased myocardial O-GlcNAc levels. Similar observations were made with dialysate from diabetic patients before exposure to rIPC (43 ± 3 vs. 16 ± 2%; P < 0.001) but no additional cardioprotection or further increase in O-GlcNAc levels was achieved by perfusion with dialysate after exposure to rIPC (44 ± 4 and 42 ± 5 vs. 43 ± 3%; P = 0.7). The glutamine:fructose-6-phosphate amidotransferase (GFAT) inhibitor azaserine abolished the cardioprotective effects and the increment in myocardial O-GlcNAc levels afforded by plasma from diabetic patients and healthy volunteers treated with rIPC.

CONCLUSIONS

rIPC and diabetes mellitus per se influence myocardial O-GlcNAc levels through circulating humoral factors. O-GlcNAc signalling participates in mediating rIPC-induced cardioprotection and maintaining a state of inherent chronic activation of cardioprotection in diabetic myocardium, restricting it from further protection by rIPC.

Improved resistance to ischemia and reperfusion, but impaired protection by ischemic preconditioning in patients with type 1 diabetes mellitus: a pilot study

Background

In patients with type 1 diabetes mellitus (T1DM), cardiovascular events are more common, and the outcome following a myocardial infarction is worse than in nondiabetic subjects. Ischemic or pharmacological preconditioning are powerful interventions to reduce ischemia reperfusion (IR)-injury. However, animal studies have shown that the presence of T1DM can limit these protective effects. Therefore, we aimed to study the protective effect of ischemic preconditioning in patients with T1DM, and to explore the role of plasma insulin and glucose on this effect.

Methods

^99mTechnetium-annexin A5 scintigraphy was used to detect IR-injury. IR-injury was induced by unilateral forearm ischemic exercise. At reperfusion, Tc-annexin A5 was administered, and IR-injury was expressed as the percentage difference in radioactivity in the thenar muscle between the experimental and control arm 4 hours after reperfusion. 15 patients with T1DM were compared to 21 nondiabetic controls. The patients were studied twice, with or without ischemic preconditioning (10 minutes of forearm ischemia and reperfusion). Patients were studied in either normoglycemic hyperinsulinemic conditions (n = 8) or during hyperglycemic normoinsulinemia (n = 7). The controls were studied once either with (n = 8) or without (n = 13) ischemic preconditioning.

Results

Patients with diabetes were less vulnerable to IR-injury than nondiabetic healthy controls (12.8 ± 2.4 and 11.0 ± 5.1% versus 27.5 ± 4.5% in controls; p < 0.05). The efficacy of ischemic preconditioning to reduce IR-injury, however, was lower in the patients and was even completely abolished during hyperglycemia.

Conclusions

Patients with T1DM are more tolerant to forearm IR than healthy controls in our experimental model. The efficacy of ischemic preconditioning to limit IR-injury, however, is reduced by acute hyperglycemia.

Trial Registration

The study is registered at www.clinicaltrials.gov (NCT00184821)

In vivo imaging of retinal ganglion cell apoptosis

Apoptosis, or programmed cell death, plays a vital role in normal development and ageing. However, dysregulation of this process is responsible for many disease states including; cancer, autoimmune and neurodegeneration. For this reason, in vivo visualisation of apoptosis may prove a useful tool for both laboratory research and clinical diagnostics. Glaucoma comprises a distinctive group of chronic optic neuropathies, characterised by the progressive loss of retinal ganglion cells (RGCs). Early diagnosis of glaucoma remains a clear and unmet need. Recently, there have been significant advances in the detection of apoptosis in vivo using fluorescent probes to visualise single RGCs undergoing apoptosis, specifically DARC (Detection of Apoptotic Retinal Cells) [1] and capQ technology [2(••)].

Ischemic preconditioning of the lower extremity attenuates the normal hypoxic increase in pulmonary artery systolic pressure

Ischemic pre-condition of an extremity (IPC) induces effects on local and remote tissues that are protective against ischemic injury. To test the effects of IPC on the normal hypoxic increase in pulmonary pressures and exercise performance, 8 amateur cyclists were evaluated under normoxia and hypoxia (13% F(I)O(2)) in a randomized cross-over trial. IPC was induced using an arterial occlusive cuff to one thigh for 5 min followed by deflation for 5 min for 4 cycles. In the control condition, the resting pulmonary artery systolic pressure (PASP) increased from a normoxic value of 25.6±2.3 mmHg to 41.8±7.2 mmHg following 90 min of hypoxia. In the IPC condition, the PASP increased to only 32.4±3.1 mmHg following hypoxia, representing a 72.8% attenuation (p=0.003). No significant difference was detected in cycle ergometer time trial duration between control and IPC conditions with either normoxia or hypoxia. IPC administered prior to hypoxic exposure was associated with profound attenuation of the normal hypoxic increase of pulmonary artery systolic pressure.

Exercise-induced cardiac preconditioning: how exercise protects your achy-breaky heart

The ability of exercise to protect the heart against ischemia-reperfusion (I/R) injury is well known in both human epidemiological studies and experimental animal models. In this review article, we describe what is currently known about the ability of exercise to precondition the heart against infarction. Just 1 day of exercise can protect the heart against ischemia/reperfusion damage, and this protection is upheld with months of exercise, making exercise one of the few sustainable preconditioning stimuli. Exercise preconditioning depends on the model and intensity of exercise, and appears to involve heightened oxidant buffering capacity, upregulated subunits of sarcolemmal ATP-sensitive potassium channels, and adaptations to cardiac mitochondria. We review the putative mechanisms involved in exercise preconditioning and point out many areas where future research is necessary to advance our understanding of how this stimulus confers resistance against I/R damage.

International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and classification of adenosine receptors--an update

In the 10 years since our previous International Union of Basic and Clinical Pharmacology report on the nomenclature and classification of adenosine receptors, no developments have led to major changes in the recommendations. However, there have been so many other developments that an update is needed. The fact that the structure of one of the adenosine receptors has recently been solved has already led to new ways of in silico screening of ligands. The evidence that adenosine receptors can form homo- and heteromultimers has accumulated, but the functional significance of such complexes remains unclear. The availability of mice with genetic modification of all the adenosine receptors has led to a clarification of the functional roles of adenosine, and to excellent means to study the specificity of drugs. There are also interesting associations between disease and structural variants in one or more of the adenosine receptors. Several new selective agonists and antagonists have become available. They provide improved possibilities for receptor classification. There are also developments hinting at the usefulness of allosteric modulators. Many drugs targeting adenosine receptors are in clinical trials, but the established therapeutic use is still very limited.

Chronic or high dose acute caffeine treatment protects mice against oleic acid-induced acute lung injury via an adenosine A2A receptor-independent mechanism

The antagonism or genetic deletion of adenosine A(2A) receptors has been shown to exacerbate tissue damage in acute lung injury. Caffeine, a widely consumed behavioral drug, acts as a non-selective antagonist of A(2A) receptor and also has additional pharmacological effects. Thus, the protective vs. deleterious effects of caffeine in acute lung injury should be evaluated. In a murine oleic acid-induced model of acute lung injury, we found that chronic caffeine treatment by drinking water (0.1g/l or 0.25g/l for 2 weeks before acute lung injury) or acute caffeine treatment at high dose (i.p. 50mg/kg, injection, 30min before acute lung injury) significantly attenuated the lung edema, hemorrhage, neutrophil recruitment as well as the inflammatory cytokine tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1) expressions in both of the wild type (WT) and A(2A) receptor knockout (KO) mice. This profile was accompanied by increased cAMP levels and up-regulation of A2B receptor mRNAs in the lungs. In contrast, acute caffeine treatment at low dose (i.p. 5mg/kg or 15mg/kg, injection, 30min before acute lung injury) enhanced the inflammation and lung damage in WT mice with decreasing cAMP but not in A(2A) receptor KO mice. These results indicate that caffeine either enhances lung damage by antagonizing A(2A) receptor or exerts protection against lung damage via A(2A) receptor-independent mechanisms, depending on the timing of exposure (chronic vs. acute) and dose of administration (low vs. high). These findings provide new insight of caffeine in acute lung injury and highlight the potential benefit and strategy of caffeine intake or administration for preventing acute lung injury.

Circulating adenosine increases during human experimental endotoxemia but blockade of its receptor does not influence the immune response and subsequent organ injury

Introduction

Preclinical studies have shown that the endogenous nucleoside adenosine prevents excessive tissue injury during systemic inflammation. We aimed to study whether endogenous adenosine also limits tissue injury in a human in vivo model of systemic inflammation. In addition, we studied whether subjects with the common 34C > T nonsense variant (rs17602729) of adenosine monophosphate deaminase (AMPD1), which predicts increased adenosine formation, have less inflammation-induced injury.

Methods

In a randomized double-blinded design, healthy male volunteers received 2 ng/kg E. Coli LPS intravenously with (n = 10) or without (n = 10) pretreatment with the adenosine receptor antagonist caffeine (4 mg/kg body weight). In addition, lipopolysaccharide (LPS) was administered to 10 subjects heterozygous for the AMPD1 34C > T variant.

Results

The increase in adenosine levels tended to be more pronounced in the subjects heterozygous for the AMPD1 34C > T variant (71 ± 22%, P=0.04), compared to placebo- (59 ± 29%, P=0.012) and caffeine-treated (53 ± 47%, P=0.29) subjects, but this difference between groups did not reach statistical significance. Also the LPS-induced increase in circulating cytokines was similar in the LPS-placebo, LPS-caffeine and LPS-AMPD1-groups. Endotoxemia resulted in an increase in circulating plasma markers of endothelial activation [intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM)], and in subclinical renal injury, measured by increased urinary excretion of tubular injury markers. The LPS-induced increase of these markers did not differ between the three groups.

Conclusions

Human experimental endotoxemia induces an increase in circulating cytokine levels and subclinical endothelial and renal injury. Although the plasma adenosine concentration is elevated during systemic inflammation, co-administration of caffeine or the presence of the 34C > T variant of AMPD1 does not affect the observed subclinical organ damage, suggesting that adenosine does not affect the inflammatory response and subclinical endothelial and renal injury during human experimental endotoxemia.

Trial Registration

ClinicalTrials (NCT): NCT00513110.

The cardiovascular effects of methylxanthines

In the concentration range that is normally achieved in humans, e.g., after the drinking of coffee or in patients treated with theophylline, the cardiovascular effects of methylxanthines are primarily due to antagonism of adenosine A(1) and A(2) receptors. Inhibition of phosphodiesterases or mobilization of intracellular calcium requires much higher concentrations. In conscious humans, acute exposure to caffeine results in an increase in blood pressure by an increased total peripheral resistance, and a slight decrease in heart rate. This overall hemodynamic response is composed of direct effects of caffeine on vascular tone, on myocardial contractility and conduction, and on the sympathetic nervous system. Caffeine is the most widely consumed methylxanthine, mainly derived from coffee intake. Regular coffee consumption can affect various traditional cardiovascular risk factors, including a slight increase in blood pressure, an increase in plasma cholesterol and homocysteine levels, and a reduced incidence of type 2 diabetes mellitus. Although most prospective studies have not reported an association between coffee consumption and coronary heart disease, these findings do not exclude that the acute hemodynamic and neurohumoral effects of coffee consumption could have an adverse effect in selected patient groups who are more vulnerable for these effects, based on their genetic profile or medication use.

Coffee and acute ischemic stroke onset: the Stroke Onset Study

OBJECTIVE

Prior research suggests an acutely elevated risk of myocardial infarction and sudden cardiac death in the hour after coffee intake. However, the risk of ischemic stroke associated with transient exposure to coffee remains unclear. We hypothesized that caffeine intake is associated with a transiently increased risk of ischemic stroke.

METHODS

In this multicenter case-crossover study, we interviewed 390 subjects (209 men, 181 women) between January 2001 and November 2006 a median of 3 days after acute ischemic stroke. Each subject's coffee consumption in the hour before stroke symptoms was compared with his or her usual frequency of consumption in the prior year.

RESULTS

Of the 390 subjects, 304 (78%) drank coffee in the prior year, 232 within 24 hours and 35 within 1 hour of stroke onset. The relative risk (RR) of stroke in the hour after consuming coffee was 2.0 (95% confidence interval [CI], 1.4-2.8; p < 0.001). There was no apparent increase in risk in the hour following consumption of caffeinated tea (RR = 0.9, 95% CI 0.4-2.0; p = 0.85) or cola (RR = 1.0, 95% CI 0.4-2.4; p = 0.95). The association between ischemic stroke in the hour after coffee consumption was only apparent among those consuming ≤1 cup per day but not for patients who consumed coffee more regularly (p for trend = 0.002). Relative risks remained similar when the sample was restricted to those who were not simultaneously exposed to other potential triggers and the results remained significant after stratifying by time of day.

CONCLUSION

Coffee consumption transiently increases the risk of ischemic stroke onset, particularly among infrequent drinkers.

Endotoxin tolerance does not limit mild ischemia-reperfusion injury in humans in vivo

Animal studies have shown that previous exposure to lipopolysaccharide (LPS) can limit ischemia-reperfusion injury. We tested whether pretreatment with LPS also protects against ischemia-reperfusion injury in humans in vivo. Fourteen volunteers received bolus injections of incremental dosages of LPS on 5 consecutive days (LPS group). Before the first and 1 day after the last LPS administration, the forearm circulation of the non-dominant arm was occluded for 10 min, with concomitant intermittent handgripping to induce transient ischemia. After reperfusion, 0.1 mg of ( 99m)Tc-labeled annexin A5 (400 MBq) was injected intravenously to detect phosphatidylserine expression as an early marker of ischemia-reperfusion injury. Similarly, the control group (n = 10) underwent the ischemic exercise twice, but without pretreatment with LPS. Annexin A5 targeting was expressed as the percentage difference in radioactivity in the thenar muscle between both hands. Endotoxin tolerance developed during 5 consecutive days of LPS administration. Annexin A5 targeting was 12.1 +/- 2.2% and 10.4 +/- 2.1% before LPS treatment at 1 h and 4 h after reperfusion, compared to 12.2 +/- 2.4% and 8.9 +/- 2.1% at 1 h and 4 h after reperfusion on day 5 (P = 1.0 and 0.6, respectively). Also, no significant changes in annexin A5 targeting were found in the control group. So, in this model, LPS-tolerance does not protect against ischemia-reperfusion injury in humans in vivo.

Long-term protection and mechanism of pacing-induced postconditioning in the heart

Brief periods of ventricular pacing during the early reperfusion phase (pacing-induced postconditioning, PPC) have been shown to reduce infarct size as measured after 2 h of reperfusion. In this study, we investigated (1) whether PPC leads to maintained reduction in infarct size, (2) whether abnormal mechanical load due to asynchronous activation is the trigger for PPC and (3) the signaling pathways that are involved in PPC. Rabbit hearts were subjected to 30 min of coronary occlusion in vivo, followed by 6 weeks of reperfusion. PPC consisted of ten 30-s intervals of left ventricular (LV) pacing, starting at reperfusion. PPC reduced infarct size (TTC staining) normalized to area at risk, from 49.0 ± 3.3% in control to 22.9 ± 5.7% in PPC rabbits. In isolated ejecting rabbit hearts, replacing LV pacing by biventricular pacing abolished the protective effect of PPC, whereas ten 30-s periods of high preload provided a protective effect similar to PPC. The protective effect of PPC was neither affected by the adenosine receptor blocker 8-SPT nor by the angiotensin II receptor blocker candesartan, but was abrogated by the cytoskeletal microtubule-disrupting agent colchicine. Blockers of the mitochondrial K_ATP channel (5HD), PKC (chelerythrine) and PI3-kinase (wortmannin) all abrogated the protection provided by PPC. In the in situ pig heart, PPC reduced infarct size from 35 ± 4 to 16 ± 12%, a protection which was abolished by the stretch-activated channel blocker gadolinium. No infarct size reduction was achieved if PPC application was delayed by 5 min or if only five pacing cycles were used. The present study indicates that (1) PPC permanently reduces myocardial injury, (2) abnormal mechanical loading is a more likely trigger for PPC than electrical stimulation or G-coupled receptor stimulation and (3) PPC may share downstream pathways with other modes of cardioprotection.

Imaging the molecular signatures of apoptosis and injury with radiolabeled annexin V

Annexin V is a ubiquitous intracellular protein in humans that has a variety of intriguing characteristics, including a nanomolar affinity for the membrane-bound constitutive anionic phospholipid known as phosphatidylserine (PS). PS is selectively expressed on the surface of apoptotic or physiologically stressed cells. As such, radiolabeled forms of annexin V have been used in both animal models and human Phase I and Phase II trials to determine if this tracer can be employed as an early surrogate marker of therapeutic efficacy in NSCLC and non-Hodgkin's lymphoma. Many other pulmonary imaging applications of radiolabeled annexin V are also possible, including the detection and monitoring of active pulmonary inflammation and other pathophysiologic stressors in a variety of diseases. In this article, the salient molecular features of apoptosis (and other forms of cell death) that permits imaging with radiolabeled annexin V will be discussed. The latest results from Phase II imaging trials with NSCLC and non-Hodgkin's lymphoma will be also be detailed. Finally, the potential future application of this tracer for the imaging of other pulmonary pathologies will be outlined.

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

Rosuvastatin increases extracellular adenosine formation in humans in vivo: a new perspective on cardiovascular protection

OBJECTIVE

Statins may increase extracellular adenosine formation from adenosine monophosphate by enhancing ecto-5'-nucleotidase activity. This theory was tested in humans using dipyridamole-induced vasodilation as a read-out for local adenosine formation. Dipyridamole inhibits the transport of extracellular adenosine into the cytosol resulting in increased extracellular adenosine and subsequent vasodilation. In addition, we studied the effect of statin therapy in a forearm model of ischemia-reperfusion injury.

METHODS AND RESULTS

Volunteers randomly received rosuvastatin or placebo in a double-blind parallel design (n=21). The forearm vasodilator response to intraarterial dipyridamole was determined in the absence and presence of the adenosine antagonist caffeine. During a separate visit the vasodilator response to nitroprusside and adenosine was established. In addition, healthy men were randomly divided in 3 groups to receive either placebo (n=10), rosuvastatin (n=22), or rosuvastatin combined with intravenous caffeine (n=12). Subsequently, volunteers performed forearm ischemic exercise. At reperfusion, Tc-99m-labeled annexin A5 was infused intravenously and scintigraphic images were acquired, providing an early marker of cell injury. Rosuvastatin treatment significantly increased the vasodilator response to dipyridamole, which was prevented by caffeine. Rosuvastatin did not influence the response to either sodium nitroprusside or adenosine indicating a specific interaction between rosuvastatin and dipyridamole, which does not result from an effect of rosuvastatin on adenosine clearance nor adenosine-receptor affinity or efficacy. Rosuvastatin increased tolerance to ischemia-reperfusion injury, which was attenuated by caffeine.

CONCLUSIONS

Rosuvastatin increases extracellular adenosine formation, which provides protection against ischemia-reperfusion injury in humans in vivo. Therefore, statins and dipyridamole may interact synergistically.

Randomized clinical trials of weight loss maintenance: a review

The problem of overweight and obesity has reached epidemic proportions in the United States and globally, and the high prevalence is due in part to the recidivism associated with weight loss treatment. Approximately one-third of lost weight is often regained in the first year after treatment and, at times, continues. Because a plethora of comorbid diseases are associated with obesity, in particular, cardiovascular disease, hypertension, and hyperlipidemia, clinicians and researchers have attempted to find useful strategies for maintaining weight loss. This review presents the findings from 42 randomized clinical trials of weight loss maintenance from 1984 through 2007 using interventions that include (1) the Internet, (2) strategies after a very low calorie diet, (3) pharmacotherapy, (4) behavioral strategies, (5) physical activity, and (6) alternative strategies. The results of the reviewed trials revealed that treatment with orlistat or sibutramine combined with dietary modification, caffeine or protein supplementation, consuming a diet lower in fat, adherence to physical activity routines, prolonged contact with participants, problem-solving therapy, and the alternative treatment of acupressure were efficacious in reducing weight regain after weight loss treatment. The limitations of some studies may reduce the robustness of their findings, and future studies are necessary to replicate and support these results so that individuals are able to maintain weight loss and retain the health benefits associated with a lower weight.

Translational imaging: imaging of apoptosis

Since its original description in 1972, apoptosis or programmed cell death has been recognized as the major pathway by which the body precisely regulates the number and type of its cells as part of normal embryogenesis, development, and homeostasis. Later it was found that apoptosis was also involved in the pathogenesis of a number of human diseases, cell immunity, and the action of cytotoxotic drugs and radiation therapy in cancer treatment. As such, the imaging of apoptosis with noninvasive techniques such as with radiotracers, including annexin V and lipid proton magnetic resonance spectroscopy, may have a wide range of clinical utility in both the diagnosis and monitoring therapy of a wide range of human disorders. In this chapter we review the basic biochemical and morphologic features of apoptosis and the methods developed thus far to image this complex process in humans.

Acrolein consumption exacerbates myocardial ischemic injury and blocks nitric oxide-induced PKCepsilon signaling and cardioprotection

Aldehydes are common reactive constituents of food, water and air. Several food aldehydes are potentially carcinogenic and toxic; however, the direct effects of dietary aldehydes on cardiac ischemia-reperfusion (IR) injury are unknown. We tested the hypothesis that dietary consumption of aldehydes modulates myocardial IR injury and preconditioning. Mice were gavage-fed the alpha, beta-unsaturated aldehyde acrolein (5mg/kg) or water (vehicle) 24h prior to a 30-min coronary artery occlusion and 24-hour reperfusion. Myocardial infarct size was significantly increased in acrolein-treated mice, demonstrating that acute acrolein exposure worsens cardiac IR injury. Furthermore, late cardioprotection afforded by the nitric oxide (NO) donor diethylenetriamine/NO (DETA/NO; dose: 0.1mg/kg x 4, i.v.) was abrogated by the administration of acrolein 2h prior to DETA/NO treatment, indicating that oral acrolein impairs NO donor-induced late preconditioning. To examine potential intracellular targets of aldehydes, we investigated the impact of acrolein on mitochondrial PKCepsilon signaling in the heart. Acrolein-protein adducts were formed in a dose-dependent manner in isolated cardiac mitochondria in vitro and specific acrolein-PKCepsilon adducts were present in cardiac mitochondrial fractions following acrolein exposure in vivo, demonstrating that mitochondria are major targets of aldehyde toxicity. Furthermore, DETA/NO preconditioning induced both PKCepsilon translocation and increased mitochondrial PKCepsilon localization. Both of these responses were blocked by acrolein pretreatment, providing evidence that aldehydes disrupt cardioprotective signaling events involving PKCepsilon. Consumption of an aldehyde-rich diet could exacerbate cardiac IR injury and block NO donor-induced cardioprotection via mechanisms that disrupt PKCepsilon signaling.