Adapting pediatric health care responses to the COVID-19 pandemic in Japan: A clinical perspective

The COVID-19 pandemic required our pediatric health care staff to adjust to many irregularities and solve serious issues in our routine clinical practice. In outpatient clinics, many children exhibited common cold symptoms that mimic COVID-19, thus we initially screened patients via an interview form, then later via SARS-CoV-2 antigen test. Cluster infections were entirely avoided by following systematic, everyday precautions. Patientsquality of life has been difficult to maintain during the pandemic, due to social and staffing restrictions. Other unexpected repercussions - such as an unexpected lack of seasonal virus infections, then a respiratory syncytial (RS) virus outbreak - required agile management of hospital resources. While we must continue to adapt our treatment programs in response to the evolving COVID-19 crisis, it remains essential to support the well-being of children through regular health check-ups, mental health support, educational opportunities, proper socialization, and close communication with parents and families.

The Protective Effects of Levetiracetam on a Human iPSCs-Derived Spinal Muscular Atrophy Model

Spinal muscular atrophy (SMA) is an inherited disease characterized by progressive motor neuron death and subsequent muscle weakness and is caused by deletion or mutation of survival motor neuron (SMN) 1 gene. Protecting spinal motor neuron is an effective clinical strategy for SMA. The purpose of this study was to investigate the potential effect of an anti-epileptic drug levetiracetam on SMA. In the present study, we used differentiated spinal motor neurons (MNs) from SMA patient-derived induced pluripotent stem cells (SMA-iPSCs) to investigate the effect of levetiracetam. Levetiracetam promoted neurite elongation in SMA-iPSCs-MNs. TUNEL-positive spinal motor neurons were significantly reduced by levetiracetam in SMA-iPSCs-MNs. In addition, the expression level of cleaved-caspase 3 was decreased by levetiracetam in SMA-iPSCs-MNs. Furthermore, levetiracetam improved impaired mitochondrial function in SMA-iPSCs-MNs. On the other hand, levetiracetam did not affect the expression level of SMN protein in SMA-iPSCs-MNs. These findings indicate that levetiracetam has a neuroprotective effect for SMA.

Efficacy of Prednisolone in Generated Myotubes Derived From Fibroblasts of Duchenne Muscular Dystrophy Patients

Duchenne muscular dystrophy (DMD) is a recessive X-linked form of muscular dystrophy characterized by progressive muscle degeneration. This disease is caused by the mutation or deletion of the dystrophin gene. Currently, there are no effective treatments and glucocorticoid administration is a standard care for DMD. However, the mechanism underlying prednisolone effects, which leads to increased walking, as well as decreased muscle wastage, is poorly understood. Our purpose in this study is to investigate the mechanisms of the efficacy of prednisolone for this disease. We converted fibroblasts of normal human cell line and a DMD patient sample to myotubes by MyoD transduction using a retroviral vector. In myotubes from the MyoD-transduced fibroblasts of the DMD patient, the myotube area was decreased and its apoptosis was increased. Furthermore, we confirmed that prednisolone could rescue these pathologies. Prednisolone increased the expression of not utrophin but laminin by down-regulation of MMP-2 mRNA. These results suggest that the up-regulation of laminin may be one of the mechanisms of the efficacy of prednisolone for DMD.

Established Stem Cell Model of Spinal Muscular Atrophy Is Applicable in the Evaluation of the Efficacy of Thyrotropin-Releasing Hormone Analog

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterized by the degeneration of spinal motor neurons. This disease is mainly caused by mutation or deletion of the survival motor neuron 1 (SMN1) gene. Currently, no effective treatment is available, and only symptomatic treatment can be provided. Our purpose in the present study was to establish a human SMA-derived induced pluripotent stem cell (SMA-iPSC) disease model and assay a therapeutic drug in preparation for the development of a novel treatment of SMA. We generated iPSCs from the skin fibroblasts of a patient with SMA and confirmed that they were pluripotent and undifferentiated. The neural differentiation of SMA-iPSCs shortened the dendrite and axon length and increased the apoptosis of the spinal motor neurons. In addition, we found activated astrocytes in differentiated SMA-iPSCs. Using this model, we confirmed that treatment with the thyrotropin-releasing hormone (TRH) analog, 5-oxo-l-prolyl-l-histidyl-l-prolinamide, which had marginal effects in clinical trials, increases the SMN protein level. This increase was mediated through the transcriptional activation of the SMN2 gene and inhibition of glycogen synthase kinase-3β activity. Finally, the TRH analog treatment resulted in dendrite and axon development of spinal motor neurons in differentiated SMA-iPSCs. These results suggest that this human in vitro disease model stimulates SMA pathology and reveal the potential efficacy of TRH analog treatment for SMA. Therefore, we can screen novel therapeutic drugs such as TRH for SMA easily and effectively using the human SMA-iPSC model. Significance: Platelet-derived growth factor (PDGF) has recently been reported to produce the greatest increase in survival motor neuron protein levels by inhibiting glycogen synthase kinase (GSK)-3β; however, motor neurons lack PDGF receptors. A human in vitro spinal muscular atrophy-derived induced pluripotent stem cell model was established, which showed that the thyrotropin releasing hormone (TRH) analog promoted transcriptional activation of the SMN2 gene and inhibition of GSK-3β activity, resulting in the increase and stabilization of the SMN protein and axon elongation of spinal motor neurons. These results reveal the potential efficacy of TRH analog treatment for SMA.

A shear-induced in vitro platelet function test can assess clinically relevant anti-thrombotic effects

Morphological features of haemostatic plugs formed in vitro under high shear forces were investigated. Electron microscopy confirmed the relevance of such haemostatic plug to a platelet-rich arterial thrombus, which is formed in vivo . In rat blood samples, the effects of anticoagulants and various antiplatelet agents on platelet reactivity (rate of haemostatic plug formation) and subsequent coagulation of the flowing blood were investigated. Haemostasis did not occur in citrated blood, and heparin greatly inhibited the shear-induced platelet reaction. Aspirin (1 mM), a thromboxane A(2) receptor antagonist (5 microM), a stable prostacyclin (0.55 nM), a stable prostaglandin E(1) (141 nM) and a phosphodiesterase inhibitor (100 microM) were tested. All these agents exerted significant inhibitory effect on shear-induced platelet reaction, including the inhibition of the very first phase of platelet plug formation, due to aggregation of shear-activated platelets. Except for the phosphodiesterase inhibitor, which prolonged clotting time, none of the above agents affected dynamic coagulation. These results suggest that the employed in vitro shear-induced thrombosis/haemostasis test can reveal in vivo the antithrombotic effect of various agents independently of their mechanism of action.

Mechanism by which a novel non-thiazolidinedione peroxisome proliferator-activated receptor gamma agonist, FK614, ameliorates insulin resistance in Zucker fatty rats

AIM

The aim of this study was to examine the mechanism by which a novel non-thiazolidinedione (TZD) peroxisome proliferator-activated receptor (PPAR) gamma agonist, FK614, ameliorates insulin resistance in Zucker fatty rats.

METHODS

FK614 (1, 3.2 or 10 mg/kg) and a TZD PPARgamma agonist, pioglitazone (1, 3.2 or 10 mg/kg), were orally administered to Zucker fatty rats (genetically obese and insulin resistant) once a day for 14 days, and an oral glucose tolerance test was performed. The expression levels of various genes in the white adipose tissue (WAT) of Zucker fatty rats treated with FK614 (3.2 mg/kg), pioglitazone (10 mg/kg) and another TZD PPARgamma agonist, rosiglitazone (3.2 mg/kg), were determined using a real-time reverse transcription-polymerase chain reaction method. Morphometric analysis of the WAT of Zucker fatty rats treated with FK614 (3.2 mg/kg) and pioglitazone (10 mg/kg) was performed. Glucose transport activity in the isolated soleus muscle of FK614-treated Zucker fatty rats was also investigated.

RESULTS

FK614 and pioglitazone both improved glucose tolerance in Zucker fatty rats. FK614 significantly increased the expression levels of acyl CoA oxidase, a PPAR-responsive gene, and adipocyte fatty acid-binding protein (aP2), an adipocyte differentiation marker gene, in epididymal WAT. It also significantly decreased the level of gene expression of tumour necrosis factor-alpha, an insulin resistance-inducing factor in retroperitoneal WAT, as did pioglitazone and rosiglitazone. FK614 and pioglitazone both significantly increased the total number of adipocytes and decreased their average size in WAT, mainly by increasing the number of small adipocytes. Additionally, administration of FK614 to Zucker fatty rats enhanced insulin sensitivity for glucose uptake in the soleus muscle.

CONCLUSION

This study suggests the possibility that FK614 induces adipocyte differentiation in Zucker fatty rats by stimulating PPARgammain vivo, thereby changing the character of WAT and improving insulin sensitivity throughout the body.

Velocity pulse advances pressure pulse by close to 45 degrees in the rat pial arterioles

In order to clarify the phase relationship between velocity pulse and pressure pulse propagating along microvessels, the red cell velocity and intravascular pressure were simultaneously measured in the rat pial arterioles of 41-53 microm in diameter with a high temporal resolution by a laser-Doppler anemometer and a servo-null micropressure system. It was found that the velocity pulse preceded the pressure pulse in all the measured arterioles by 18.7-35.6 ms. The corresponding phase difference was 43.6+/-6.9 degrees (mean +/- SD), which is not statistically different from 45 degrees. The value is consistent with the phase difference predicted for the blood flow in microvessels with a small reflection coefficient at frequencies as low as the heart rate of the rats. The present results suggest that the upstream changes in blood flow are transmitted by the velocity pulse faster than by the pressure pulse in the microvasculature.

Tomatoes have natural anti-thrombotic effects

The prevention of arterial thrombotic diseases has a high priority in developed countries. An inappropriate diet may be an important risk factor for thrombotic events. The daily intake of an anti-thrombotic diet may offer a convenient and effective way of prevention. The aim of the present study was to test tomato extracts for anti-thrombotic effects and to identify those varieties that have such an effect. A shear-induced platelet-function test (haemostatometry) was used to test anti-thrombotic potential in vitro. Extracts from those tomato varieties that showed a significant anti-thrombotic activity in vitro were further assessed in vivo, using a laser-induced thrombosis test in mice. One tomato variety (KG99-4) showed significant anti-thrombotic activity both in vitro and in vivo. KG99-4 inhibited not only platelet-rich thrombus formation but also had a thrombolytic effect. It is concluded that haemostatometry can detect and classify the anti-thrombotic potential of fruits and vegetables and offers a simple way of screening for such effects.

There is no valid evidence presented as to an impaired endothelial NO system in the stroke-prone spontaneously hypertensive rats

Platelet reactivity in stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY) were compared. In vivo platelet reactivity was tested by the He-Ne laser-induced thrombosis model. The number of laser pulses needed to reach thrombotic occlusion of the targeted vessel was used as an index of thrombogenicity. SHRSP rats needed significantly less number of irradiation to reach occlusion than WKY rats (SHRSP vs. WKY, 5.1+/-0.3 vs. 8.1+/-0.6), indicating enhanced thrombotic response in SHRSP rats. Further, acetylcholine administration significantly increased the number of laser pulses until occlusion in WKY but not in SHRSP rats. This suggests an impaired thrombotic reaction in acetylcholine-treated WKY but not in SHRSP rats. Platelet reactivity in vitro was measured in native blood by a shear-induced haemostasis test (haemostatometry). Indexes of this test (H1/H2), which inversely correlated with platelet reactivity, were significantly greater in SHRSP than in WKY rats (SHRSP vs. WKY, H1: 1815+/-192 vs. 763+/-75; H2: 7547+/-723 vs. 3536+/-264). This suggests reduced platelet reactivity in SHRSP compared with WKY rats. Thus, the present findings show increased thrombotic tendency in SHRSP rats in vivo despite reduced platelet reactivity in vitro. To explain this contradiction, we suggest that an increased in vivo thrombotic tendency may be due to impaired nitric oxide (NO) release from endothelial cells in SHRSP rats, and that a reduced platelet reactivity in vitro may be due to an adaptation of SHRSP rats to survive at extremely high blood pressure.

FR183998, a Na+/H+ exchange inhibitor, suppresses both IL-8 content and myocardial infarct size in a cardiac ischaemia-reperfusion model in rats

The aim of this study was to determine the effect of FR183998 (5-(2,5-dichlorothiophen-3-yl)-3-[(2-dimethylaminoethyl)carbamoyl]benzoylguanidine dihydrochloride), an Na+/H+ exchange inhibitor, on myocardial interleukin-8 (IL-8) content and myocardial infarct size in a rat ischaemia and reperfusion model. Rats underwent 30 min of ischaemia followed by 1 to 24 h of reperfusion. IL-8 content rapidly increased in reperfused rat hearts. The maximum increase in IL-8 was obtained after 3 h of reperfusion. Intravenous administration of FR183998 at 1 and 3.2 mg kg(-1), 5 min before ischaemia, significantly reduced the IL-8 level after 3 h of reperfusion (122 +/- 16 and 149 +/- 23 pg mg(-1) protein, respectively), compared with that of the saline-treated group (258 +/- 27 pg mg(-1) protein). Myeloperoxidase activity after 3 h of reperfusion was also reduced by FR183998 (from 0.83+0.19 unit g(-1) weight of tissue in the saline-treated group to 0.36 +/- 0.09 and 0.33 +/- 0.06 unit g(-1) weight of tissue in FR183998-treated groups at 1.0 and 3.2 mg kg(-1), respectively). Myocardial infarction induced by 30 min of ischaemia and 24 h of reperfusion was significantly suppressed by the same doses of FR183998 (14.0 +/- 1.5,13.5 +/- 1.9% at 1.0 and 3.2 mg kg(-1)), compared with 22.2+2.7% in the saline-treated group. These results suggestthat IL-8 may contribute to the generation of myocardial infarction in an ischaemia and reperfusion model in rats.

Cerebral thrombosis and microcirculation of the rat during the oestrous cycle and after ovariectomy

1. The effects of oestrogen on thrombogenesis and the cerebral microcirculation of the female rat were studied during the oestrous cycle and after ovariectomy. 2. Serum levels of oestradiol (E2) and plasma concentrations of nitric oxide (NO) metabolites were significantly greater at pro-oestrus than at dioestrus. Blood vessel diameter, mean red cell velocity, wall shear rate and blood flow at pro-oestrus were significantly higher than at dioestrus. Thrombotic tendency, assessed using a He-Ne laser-induced thrombosis model, was significantly decreased at pro-oestrus compared with dioestrus. 3. The long-term deprivation of oestrogen by ovariectomy significantly depressed serum levels of E2 and plasma concentrations of NO metabolites. Thrombotic tendency was significantly increased 4 weeks after ovariectomy. Vessel diameter, mean red cell velocity, wall shear rate and blood flow in pial arterioles were significantly reduced after ovariectomy. 4. Exogenous administration of oestrogen (17 beta-oestradiol) after surgery reversed the increased thrombotic tendency mediated by ovariectomy. 5. These results strongly indicate that oestrogen mediates beneficial effects on the cerebral microcirculation and moderates cerebral thrombotic mechanisms in the female rat.

Effect of FR194738, a potent inhibitor of squalene epoxidase, on cholesterol metabolism in HepG2 cells

(E)-N-ethyl-N-(6,6-dimethyl-2-hepten-4-ynyl)-3-[2-methyl-2-(3-thienylmethoxy)propyloxy]benzylamine hydrochloride (FR194738) inhibited squalene epoxidase activity in HepG2 cell homogenates with an IC50 value of 9.8 nM. In the study using intact HepG2 cells, FR194738 inhibited cholesterol synthesis from [14C]acetate with an IC50 value of 4.9 nM, and induced intracellular [14C]squalene accumulation. On the other hand, the 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitor simvastatin reduced both cholesterol and squalene synthesis from [14C]acetate. Incubation with simvastatin for 18 h produced increases in HMG-CoA reductase activity in HepG2 cells, which was related to the degree of reduction in cholesterol synthesis. The HMG-CoA reductase activity increased by 13- and 19-fold at the concentrations of simvastatin that inhibited cholesterol synthesis by 65% and 82%, respectively. In contrast, FR194738 did not increase HMG-CoA reductase activity at the concentrations that inhibited cholesterol synthesis by 24% and 69%, and moderate increase (4.6-fold) was observed at the concentration that inhibited cholesterol synthesis by 90%. These results suggest that non-sterol metabolite(s) derived from mevalonate prior to the squalene epoxidation step in the cholesterol synthetic cascade have a regulatory role in the suppression of HMG-CoA reductase activity. We speculate that FR194738 inhibits cholesterol synthesis with a minimal change of the regulator(s) and would be highly effective in the treatment of hypercholesterolemia.

Reciprocal regulation of cyclic GMP content by cyclic GMP-phosphodiesterase and guanylate cyclase in SHR with CsA-induced nephrotoxicity

1. The effect of the immunosuppressant drug, cyclosporin A (CsA), on the nitric oxide (NO)-cyclic GMP pathway was examined in spontaneous hypertensive rats (SHR). 2. CsA (50 mg kg(-1)) treatment for 14 days induced typical CsA nephrotoxicity, which was characterized by morphological changes in the glomerulus and proximal tubule as well as an abnormality of creatinine clearance, FENa and BUN. 3. CsA significantly decreased both NOS activity in the kidney and NOx contents in urine, but significantly increased cyclic GMP content in the kidney. 4. A marked change in two kinds of enzyme, which contribute towards the increase in cyclic GMP in tissue, namely, a decrease in cyclic GMP-phosphodiesterase activity and increase in guanylate cyclase activity, was observed in the kidney treated with CsA. 5. In the isolated perfused kidney, a decreased in perfusion pressure induced by SNP in the kidney isolated from CsA group was significantly greater than that of control. 6. There seem to exist a reciprocal mechanism to maintain cyclic GMP content via both a decrease in cyclic GMP degradation and an increase in synthesis of cyclic GMP in the kidney treated with CsA. This mechanism is likely to be playing an important role to regulate the homeostasis in the kidney with CsA nephrotoxicity.

Effects of vitamin E and sesamin on hypertension and cerebral thrombogenesis in stroke-prone spontaneously hypertensive rats

The preventive effects of sesamin, a lignan from sesame oil, and vitamin E on hypertension and thrombosis were examined using stroke-prone spontaneously hypertensive rats (SHRSP). At 5 weeks of age the animals were separated into four groups: (i) a control group; (ii) a vitamin E group, which was given a 1,000 mg alpha-tocopherol/kg diet; (iii) a sesamin group, given a 1,000 mg sesamin/kg diet; and (iv) a vitamin E plus sesamin group, given a 1,000 mg alpha-tocopherol plus 1,000 mg sesamin/kg diet for 5 weeks from 5 to 10 weeks of age. Resting blood pressure was measured by the tail-cuff method once weekly. A closed cranial window was created and platelet-rich thrombi were induced in vivo using a helium-neon laser technique. The number of laser pulses required for formation of an occlusive thrombus was used as an index of thrombotic tendency. In control rats, systolic blood pressure and the amount of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) became significantly elevated with age. However, the elevation in blood pressure and 8-OHdG were significantly suppressed in rats administrated vitamin E, sesamin, or vitamin E plus sesamin. At 10 weeks, the number of laser pulses required to induce an occlusive thrombus in arterioles of the control group was significantly lower than in the other groups (p<0.05). These results indicate that chronic ingestion of vitamin E and sesamin attenuated each of elevation in blood pressure, oxidative stress and thrombotic tendency, suggesting that these treatments might be beneficial in the prevention of hypertension and stroke.

FR226807: a potent and selective phosphodiesterase type 5 inhibitor

We describe the pharmacological characteristics of a novel phosphodiesterase type 5 inhibitor FR226807, N-(3,4-dimethoxybenzyl)-2-[[(1R)-2-hydroxy-1-methylethyl]amino]-5-nitrobenzamide. FR226807 inhibited phosphodiesterase type 5 isolated from human platelets with an IC(50) value of 1.1 nM. FR226807 also inhibited phosphodiesterase type 6 with an IC(50) of 20 nM; however, the IC(50) value for phosphodiesterase type 6 was 18-fold higher than that for phosphodiesterase type 5. The IC(50) values of FR226807 for other phosphodiesterases (phosphodiesterase type 1, phosphodiesterase type 2, phosphodiesterase type 3, and phosphodiesterase type 4) were 1000-fold higher than that for phosphodiesterase type 5. FR226807 increased the cyclic guanosine monophosphate (cGMP) content in corpus cavernosum isolated from rabbit, an effect associated with relaxation of the muscle. FR226807 enhanced the relaxation response induced by electrical field stimulation of corpus cavernosum isolated from the rabbit. In an anesthetized dog model for the evaluation of erectile function, intravenous administration of FR226807 prolonged the time to return to 75% of maximal intracavernosal pressure after cessation of electrical stimulation of the pelvic nerve. In summary, FR226807 is a potent and highly selective phosphodiesterase type 5 inhibitor with an augmentative effect on penile erection and will be useful for the treatment of erectile dysfunction.

Protective effect of FR183998, a Na+/H+ exchange inhibitor, against postischemic injury after normothermic and prolonged hypothermic ischemia in isolated perfused rat hearts

Inhibition of Na+/H+ exchanger has been reported to protect hearts from ischemia and reperfusion injury. However, the effect of Na+/H+ exchange inhibition on hypothermic ischemic injury has not been extensively studied and the results are inconsistent. The purpose of this study was to investigate whether inhibition of Na+/H+ exchange with FR183998 (5-(2,5-dichlorothiphen-3-yl)-3-[(2-dimethylaminoethyl)carbamoyl]benzoylguanidine dihydrochloride), a potent Na+/H+ exchange inhibitor, would show protective effects against postischemic cardiac dysfunction after hypothermic as well as normothermic ischemia and furthermore, after hypothermic cardioplegic arrest in isolated rat hearts. FR183998 (3.2 x 10(-8)-3.2 x 10(-7) M) improved post-ischemic recovery of left ventricular developed pressure and suppressed the increase of left ventricular end diastolic pressure in a dose-dependent manner, after not only 45 min of normothermic ischemia but also 6 h of hypothermic ischemia. Furthermore, FRI 83998 (10(-7)-10(-6) M) significantly reduced creatine kinase release during reperfusion after 3 h of hypothermic ischemia with cardioplegia. These results indicate that FR183998 has a potent protective effect on postischemic cardiac dysfunction after normothermic and hypothermic ischemia, and also on reperfusion injury after hypothermic cardioplegic arrest, suggesting that its effect would be additive to cardioplegia.

Induction of choleresis by immunosuppressant FK506 through stimulation of insulin-like growth factor-I production in the liver of rats

FK506 (Tacrolimus) is an effective immunosuppressant currently used worldwide in organ transplantation. Based on our recent findings that insulin-like growth factor-I (IGF-I) is important for the stimulation of choleresis in vivo, in this study we investigated the effect of FK506 on bile flow and the plasma and hepatic levels of IGF-I in rats. Intravenous treatment of rats with FK506 resulted in a significant increase in bile flow, whereas cyclosporin A induced a significant decrease. A significant increase in plasma levels of IGF-I was observed in rats 30 min after a single intravenous administration of FK506. Oral treatment of rats with FK506 for 1 week also resulted in an increase in both plasma and hepatic levels of IGF-I. Overall, this study showed that FK506 treatment increased bile flow and also induced an increase in the plasma and hepatic levels of IGF-I in rats, suggesting that a stimulation of hepatic IGF-I production by FK506 may contribute to its choleretic profile.

Amelioration of insulin resistance in diabetic ob/ob mice by a new type of orally active insulin-mimetic vanadyl complex: bis(1-oxy-2-pyridinethiolato)oxovanadium(IV) with VO(S(2)O(2)) coordination mode

Recently, we have shown that a newly synthesized vanadyl complex, bis(1-oxy-2-pyridinethiolato)oxovanadium(IV), VO(opt)(2), is a potent orally active insulin-mimetic in treating streptozotocin-induced diabetes in rats, with long-term action. In the present study, the anti-diabetic effect of VO(opt)(2) and its mechanism in ob/ob mice, an obese non-insulin-dependent diabetes mellitus (NIDDM) animal model, was investigated. In ob/ob mice, 15-day oral treatment with VO(opt)(2) resulted in a dose-dependent decrease in the levels of glucose, insulin and triglyceride in blood. VO(opt)(2) was also effective in ameliorating impaired glucose tolerance in ob/ob mice, when an oral glucose tolerance test was performed after treatment with VO(opt)(2). Tumor necrosis factor-alpha (TNF-alpha) is a key component of obesity-diabetes link, we therefore examined the attenuating effect of VO(opt)(2) on impaired insulin signal transduction induced by TNF-alpha. Elevated expression of TNF-alpha was observed in the epididymal and subcutaneous fat tissues of ob/ob mice. Incubation of 3T3-L1, mouse adipocytes, with TNF-alpha reduced the phosphorylation of insulin receptor substrate-1 (IRS-1), whereas VO(opt)(2) treatment resulted in an enhancement of IRS-1 phosphorylation, irrespective of the presence or absence of TNF-alpha. Overall, the present study demonstrates that VO(opt)(2) exerts an anti-diabetic effect in ob/ob mice by ameliorating impaired glucose tolerance, and furthermore, attenuates the TNF-alpha-induced decrease in IRS-1 phosphorylation in adipocytes. These results suggest that the anti-diabetic action of VO(opt)(2) is derived from an attenuation of a TNF-alpha induced impaired insulin signal transduction via inhibition of protein tyrosine phosphatase, providing a potential clinical utility for VO(opt)(2) in the treatment of NIDDM.

Maximal flow pulsation in the pial arterioles of rats at increased intracranial pressure

Red cell velocity in the brain pial arterioles ( 12-58 microm in diameter) of rats was measured by a fiber-optic laser-Doppler anemometer microscope to study the effects of intracranial pressure (ICP) on flow pulsation. The amplitude of velocity pulsation in the pial arterioles was 24+/-9% (mean +/- SD) of the temporal mean velocity under normal physiological conditions (ICP = 5 mmHg). It increased gradually up to 40+/-11% with increasing ICP up to 50 mmHg on average. It also increased with the vessel diameter at fixed values of ICP. In each arteriole, the velocity amplitude increased steeply at a critical value of ICP as ICP increased. The critical value of ICP ranged between 20 and 40 mmHg,. increased with the vessel diameter, and decreased downstream along arterial trees. These results suggest a correlation between the critical ICP and the internal pressure of the pial arteriole.

The effects of zenarestat, an aldose reductase inhibitor, on minimal F-wave latency and nerve blood flow in streptozotocin-induced diabetic rats

The effects of zenarestat, 3-(4-bromo-2-fluorobenzyl)-7-chloro-3,4-dihydro-2,4-dioxo-1(2H)-quinazolineacetic acid, an aldose reductase inhibitor (ARI), on F-wave conduction abnormalities, nerve blood flow (NBF) reduction and sorbitol accumulation were studied in streptozotocin-induced diabetic rats. Two weeks after the induction of diabetes, zenarestat was given once a day for two weeks. In diabetic control rats, marked accumulation of sorbitol, reduction of NBF and prolongation of minimal F-wave latency (FWL) were observed as compared to normal rats. Zenarestat, at a dose of 32 mg/kg, inhibited sorbitol concentration to nearly the normal rat level and significantly improved not only NBF but also minimal FWL. At a dose of 3.2 mg/kg, sorbitol accumulation was inhibited by approximately 40% and there was a tendency to increase in NBF; however, minimal FWL was not improved at all. These data suggest that a highly inhibition of the nerve sorbitol accumulation is requisite for the treatment of diabetic peripheral neuropathy.

A novel pyridazinone derivative as a nonprostanoid PGI2 agonist

A novel optically pure pyridazinone derivative was synthesized and identified as a nonprostanoid PGI2 agonist. It inhibited ADP-induced aggregation of human platelets with an IC50 value of 0.081 microM and has high oral bioavailability (56%) with a long half-life (4.3 h) in rats.

The effects of zenarestat, an aldose reductase inhibitor, on peripheral neuropathy in Zucker diabetic fatty rats

We studied the effects of zenarestat, an aldose reductase inhibitor (ARI), on peripheral neuropathy in Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes. ZDF rats and their lean rats counterparts were fed a sucrose-containing diet, and zenarestat was given orally once a day for 8 weeks. Motor nerve conduction velocity (MNCV), F-wave minimal latency (FML), and sorbitol concentrations in the sciatic nerve were measured. In ZDF control rats, a remarkable accumulation of sorbitol, a delay in FML, and a slowing of MNCV were observed compared with lean rats. At a dose of 3.2 mg/kg, zenarestat had no significant effect on the delay in FML and the slowing of MNCV, although the sorbitol accumulation in the sciatic nerve was partially inhibited in ZDF rats. On the other hand, 32 mg/kg zenarestat treatment improved these nerve dysfunctions in ZDF rats, along with a reduction of nerve sorbitol accumulation almost to the level of lean rats. These data showed that zenarestat improved diabetic peripheral neuropathy in ZDF rats, a type 2 diabetes model, providing evidence for the therapeutic potential of zenarestat for the treatment of diabetic neuropathy.

Inhibitory effect of various thrombin inhibitors on shear-induced platelet function and dynamic coagulation

We assessed the effects of active site-directed, fibrinogen recognition exosite (FRE)-directed and bifunctional thrombin inhibitors, on shear-induced platelet reactivity (adhesion/aggregation) and dynamic coagulation (coagulation of flowing blood). An in vitro test for shear-induced haemostatic plug formation and dynamic coagulation (haemostatometry) was employed using non-anticoagulated rat blood. The active site-directed inhibitors (argatroban, P891, P899) caused inhibition of platelet reactivity and coagulation at 1-, 100- and 100-microM concentrations, respectively. Bifunctional inhibitors (P553, P1053) exerted inhibitory effects at 0.1 microM. A dimeric bifunctional inhibitor P824 caused significant inhibition at 1 microM. The FRE-directed inhibitor (P960) inhibited shear-induced platelet reactivity at 10 microM but the dynamic coagulation at 1 microM. Combination of active site-directed argatroban and FRE-directed P960 did not show any synergistic effect. The most potent inhibition was observed in monomeric bifunctional inhibitors. The inhibitory effects were compared with the K(i) values against human thrombin and with the IC(50) values against fibrin clot formation. The minimum effective concentrations on shear-induced platelet reactivity and dynamic coagulation were comparable with the IC(50) values, but not with the K(i) values.

Lesser reduction in bone mineral density by the immunosuppressant, FK506, compared with cyclosporine in rats

BACKGROUND

Posttransplantation osteopenia leading to osteoporosis induced commonly by treatment with immunosuppressants including cyclosporine (CsA) is a severe complication and results in lowering the quality of life in patients receiving organ transplantation. FK506 is a newly developed immunosuppressant and is currently being used for the prevention of rejection after organ transplantation. In this study, to investigate whether FK506 as well as CsA would cause osteopenia or not, we evaluated the effect of FK506 on bone mineral density and several parameters relevant to bone metabolism in comparison with that of CsA using normal rats.

METHODS

Ten-week-old male Sprague-Dawley rats were treated with FK506 (vehicle, 1 mg/kg, and 3.2 mg/kg) or CsA (vehicle, 10 mg/kg, and 32 mg/kg) by daily oral gavage for 28 days. Bone mineral density of the femur, plasma insulin-like growth factor I (IGF-I), and urinary deoxypyridinoline were determined by peripheral quantitative computerized tomography, radioimmunoassay, and enzyme-linked immunosorbent assay, respectively.

RESULTS

The reduction in bone mineral density of the femur was observed in both FK506- and CsA-treated rats. The reduction in CsA-treated rats, however, was statistically significant and strikingly severe, whereas that in FK506-treated rats was much less severe than CsA. Plasma IGF-I levels were significantly elevated in FK506-treated rats but not in CsAtreated rats. Urinary deoxypyridinoline levels were unchanged in FK506-treated rats but elevated in CsA-treated rats.

CONCLUSIONS

Compared with CsA, FK506 does not appear to induce severe osteopenia by high-turnover bone metabolism in the rat by mediating via IGF-I induction in part. The results suggest that FK506 may exert favorable effects on bone metabolism in patients with organ transplantation compared with CsA. To assess this idea, further clinical investigations focused on bone metabolism will be required.

Effects of clopidogrel on platelet activation and coagulation of non-anticoagulated rat blood under high shear stress

Clopidogrel is a new thienopyridine derivative similar to ticlopidine, which inhibits adenosine diphosphate-induced platelet aggregation. The in vitro effects of clopidogrel on shear-induced platelet activation and coagulation were assessed after oral administration to rats, by subjecting non-anticoagulated blood to haemostatometry. Clopidogrel significantly inhibited shear-induced platelet activation and coagulation 2 h after administration at doses of 7.5 and 15 mg/kg. Both ticlopidine (200 mg/kg) and aspirin (200 mg/kg) inhibited shear-induced platelet activation, but not coagulation. The peak inhibition of plaetelet activation by clopidogrel occurred 2 h after oral administration, but significant inhibition persisted even after 24 h. These results suggest that clopidogrel could be a more potent antithrombotic agent than ticlopidine or aspirin, and also that ADP plays an important role in shear-induced platelet activation.

Stimulation of choleresis by insulin-like growth factor-I in rats

Insulin-like growth factor-I (IGF-I) is an endogenous growth factor which is mainly produced in the liver. The functions of IGF-I can be summarized as growth-promoting and insulin-like metabolic actions. In the present study, the effect of IGF-I on bile flow and bile acid secretion was investigated in rats. In normal rats bile flow was significantly increased by single exogenous administration of IGF-I, and by 1 week treatment of IGF-I, both bile flow and bile acid secretion were significantly increased. Moreover, to further understand the relationship between IGF-I and bile acid secretion, hypophysectomized rats were next used. We found that the decreases in bile flow and bile acid secretion observed in rats after hypophysectomy, as well as the decrease in the endogenous level of IGF-I in the blood, were partially reversed by 1 week exogenous IGF-I treatment. Overall, this study showed that IGF-I stimulates choleresis associated with an elevation of bile acid secretion in both normal and hypophysectomized rats when exogenously administered, suggesting the importance of IGF-I in the stimulation of choleresis in vivo.

Protective effects of imidapril on He-Ne laser-induced thrombosis in cerebral blood vessels of stroke-prone spontaneously hypertensive rats

Inhibitors of angiotensin converting enzyme (ACE) have been developed recently for therapeutic purposes in hypertension and ischemic cardiovascular diseases. Ogiku et al. reported that one such inhibitor, imidapril, significantly prolonged survival in stroke-prone spontaneously hypertensive rats (SHRSP). The present study was designed to investigate the effect of imidapril on cerebral blood vessels in SHRSP to clarify role of the ACE inhibitor in mechanisms of cerebral thrombosis and stroke. Imidapril was administered orally at 1.0 and 5.0 mg/kg/day for 3 weeks from the age of 7 weeks, and was shown to prevent the usual increase in blood pressure seen in these animals. It also delayed He-Ne laser-induced cerebral thrombosis and increased significantly the plasma concentration of nitric oxide metabolites (NO2/NO3). To confirm the association between nitric oxide (NO) and these effects of imidapril, an inhibitor of nitric oxide synthase, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) was dissolved in drinking water and administered to the animals for 3 weeks. Four of six rats died from stroke when L-NAME was given alone. When imidapril (5.0 mg/kg/day) was administered with L-NAME, however, the animals showed no signs or symptoms of stroke. In these instances, therefore, the concurrent administration of L-NAME with imidapril reversed significantly the effects of imidapril. Intravenous injection of imidaprilat (100 microg/kg), an active metabolite of imidapril, also decreased blood pressure significantly and increased the plasma levels of NO2/NO3 after 5 min. Moreover, imidaprilat enlarged arteriolar diameters and caused an increase in red cell velocity and mean blood flow in pial arterioles after 15 min. The results strongly suggested that imidapril protects cerebral vessels in SHRSP by elevating the release of NO, thereby improving the cerebral circulation and reducing the tendency to thrombosis and stroke.

Probable involvement of the 5-hydroxytryptamine(4) receptor in methotrexate-induced delayed emesis in dogs

Delayed emesis in cancer patients undergoing chemotherapy remains a significant problem. The pathogenesis of delayed emesis is still obscure. It was recently demonstrated that methotrexate (MTX), an anticancer drug, evoked delayed emesis in dogs in a manner similar to its actions in humans. We evaluated the antiemetic activity of FK1052, a potent antagonist for both the 5-hydroxytryptamine (HT)(3) and 5-HT(4) receptors, on delayed emesis induced by MTX in beagle dogs. Animal behavior was recorded for 3 days using a video camera. Delayed emesis lasting up to 72 h was observed in dogs treated with MTX (2.5 mg/kg i.v.), but acute emesis did not occur. The following antiemetics, at the dose that prevents cisplatin-induced acute emesis in dogs, were administered i.v. as multiple injections every 12 h during days 2 to 3. FK1052 (1 and 3.2 mg/kg) significantly reduced the emetic episodes caused by MTX, whereas ondansetron (1 mg/kg), a selective 5-HT(3) receptor antagonist, was not effective. The emetic episodes induced by MTX were also inhibited by another 5-HT(3/4) receptor antagonist, tropisetron (1 mg/kg). CP-122,721 (0. 1 mg/kg), a potent selective tachykinin NK(1) receptor antagonist, significantly reduced the emetic responses to MTX. Copper sulfate-induced emesis in dogs was also prevented by FK1052, tropisetron, and CP-122,721 but not by ondansetron. FK1052, tropisetron, and ondansetron had negligible affinity for the NK(1) receptor at 1 microM. These results suggest that the 5-HT(4) receptor may be in part involved in the production of delayed emesis induced by MTX in dogs and that FK1052 may be a useful drug against both acute and delayed emesis induced by cancer chemotherapy.

Preischemic and postischemic treatment with a new Na+/H+-exchange inhibitor, FR183998, shows cardioprotective effects in rats with cardiac ischemia and reperfusion

This study describes the pharmacologic profile of a new Na+/H(+)-exchange inhibitor, FR183998, in anesthetized rats. FR183998 had a potent inhibitory effect on Na+/H+ exchange of rat lymphocytes with median inhibitory (IC50) value of 0.3 nM. Treatment with FR183998 (0.01-0.32 mg/kg, i.v.) reduced or completely abolished ventricular fibrillation and mortality induced by 5-min ischemia followed by reperfusion, when it was administered not only 5 min before ischemia but also 1 min before reperfusion. Myocardial infarct size induced by 30-min ischemia and 60-min reperfusion was reduced significantly in a dose-dependent manner by FR183998 (0.1-1.0 mg/kg, i.v.) when the drug was administered preischemically or at an early phase of ischemia. The ventricular tachycardia and the ventricular fibrillation observed during the ischemic period also were suppressed significantly. These results indicate that FR183998 has a strong inhibitory effect on Na+/H+ exchange and suggest that treatment with FR183998 either before or immediately after the onset of ischemia can prevent the occurrence of arrhythmias and myocardial cell necrosis in situations of ischemia and reperfusion.

In vitro antiplatelet profile of FR171113, a novel non-peptide thrombin receptor antagonist

Synthetic peptides (5 to 14 amino acids), identical in sequence to the new amino-terminus of the thrombin receptor generated following cleavage by thrombin, act as thrombin receptor agonist peptides. Whilst thrombin receptor antagonist peptides are known, non-peptide thrombin receptor antagonists have yet to be described. In the present study, we compared the antiplatelet effects of 3-(4-chlorophenyl)-2-(2,4-dichlorobenzoylimino)-5-(methoxycarbonyl methylene)-1,3-thiazolidin-4-one (FR171113), a novel non-peptide thrombin receptor antagonist, with the known thrombin receptor antagonist 3-mercapto-propionyl-Phe-Cha-Cha-Arg-Asn-Pro-Asn-Asp-Lys-Tyr-OH (C186-65), and argatroban, a specific protease inhibitor of thrombin. FR171113 and C186-65 inhibited thrombin-induced platelet aggregation (IC(50)=0.29 microM and 15 microM, respectively) and Ser-Phe-Leu-Leu-Arg-Asn-NH(2) [a synthetic thrombin receptor agonist peptide (TRAP-6)] induced platelet aggregation (0.15 microM and 20 microM, respectively) in human washed platelets. Argatroban potently inhibited thrombin-induced platelet aggregation (IC(50)=3.5 nM), but did not inhibit TRAP-6-induced aggregation even at 100 microM. In contrast, these compounds did not show inhibitory effects on ADP- and collagen-induced aggregation in human platelet-rich plasma even at 100 microM. FR171113 caused a parallel shift to the right of the concentration-response curve describing aggregation induced by TRAP-6. The Schild plot of the data had a slope of -0.840 (r=0.98) and the pA(2) was 7.29. In protease activity studies using a chromogenic substrate, argatroban inhibited thrombin protease activity in a dose-dependent manner, whereas FR171113 and C186-65 were inactive, even at 100 microM. Additionally, only argatroban displayed dose-dependent prolongation of thrombin time, activated partial thromboplastin time and prothrombin time. FR171113 and C186-65 showed no effects, even at a concentration of 100 microM. These results suggest that FR171113 has a similar mode of action to C186-65, but with more potent antiplatelet activity. In conclusion, FR171113 is suggested to be the first example of a non-peptide thrombin receptor antagonist.

Synthesis and biological activity of 4-methyl-3,5-dioxane derivatives as thromboxane A2 receptor antagonists

The synthesis and biological activity of novel 4-methyl-3,5-dioxane analogues are described. All compounds were produced through modification of the substituent formally corresponding to the omega-octenol side chain of thromboxane A2 (TXA2), in reference to the structure of SQ29548. Several compounds were found to be potent TXA2 receptor antagonists. Compound 8b was the most effective inhibitor of 9,11-epoxymethano PGH2 (U-46619)-induced human platelet aggregation (IC50 = 7.4 nM).

Effects of intracranial pressure on the pial microcirculation in rats studied by a fiber-optic laser-Doppler anemometer microscope

The fiber-optic laser-Doppler anemometer microscope (FLDAM) developed in our laboratory was applied to measure red cell velocity in individual pial microvessels in rats to determine the effect of intracranial pressure (ICP) on the pial microcirculation. The red cell velocity and the vessel diameter of pial microvessels were measured through a closed cranial window at controlled values of ICP between 0 and 50 mmHg. As ICP increased from 0 to 50 mmHg, the average relative diameter of venules with respect to the diameter at an ICP of 5 mmHg decreased from 1.18 +/- 0.12 (mean +/- SD) to 0.74 +/- 0.08 and the average relative velocity increased from 0.80 +/- 0.20 to 1.83 +/- 0.42 monotonically. The changes in diameter and velocity of arterioles with ICP were small, and they were not significantly different from those values at an ICP of 5 mmHg except for the diameter at an ICP of 20 mmHg. The mean volume flow rates calculated assuming a circular vessel cross-section did not show any statistically significant change with ICP between 0 and 50 mmHg in both arterioles and venules, which supports the concept of autoregulation.

Protective effect of FR168888, a new Na+/H+ exchange inhibitor, on ischemia and reperfusion-induced arrhythmia and myocardial infarction in rats: in comparison with other cardioprotective compounds

We have studied the effects of FR168888 (5-hydroxymethyl-3-(pyrrol-1-yl)benzoylguanidine methanesulfonate), a new Na+/H+ exchange inhibitor, on ischemia and reperfusion-induced arrhythmia and myocardial infarction in anesthetized rats and compared them with those of other cardioprotective compounds. FR168888 had a potent inhibitory effect on Na+/H+ exchange of rat lymphocytes acidified with Na+-propionate with a Ki value of 6.4 nM. Pretreatment with FR168888 (0.032-0.32 mg/kg, i.v.) reduced or completely abolished the ventricular fibrillation (VF) induced by reperfusion after 5 min of regional ischemia, while lidocaine, a class I antiarrhythmic agent, showed less effect against VF as compared with FR168888. The size of myocardial infarction induced by 60-min ischemia and 60-min reperfusion was attenuated by FR168888 dose-dependently (1.0-10 mg/kg, i.v.), and ventricular tachycardia and VF were significantly reduced during the ischemic period. In contrast, propranolol and diltiazem did not show such protective effects on myocardial infarct size. In addition, FR168888 did not change hemodynamic parameters in rats. These results indicate that FR168888 has a strong inhibitory effect on Na+/H+ exchange and that treatment with FR168888 can protect the heart from arrhythmia and myocardial cell death in ischemic and reperfused situations.

Effects of voluntary exercise and L-arginine on thrombogenesis and microcirculation in stroke-prone spontaneously hypertensive rats

1. The preventive effects of exercise and L-arginine intake on hypertension and thrombosis in stroke-prone spontaneously hypertensive rats (SHRSP) were studied. 2. Stroke-prone spontaneously hypertensive rats were divided into three groups: (i) the control, sedentary group; (ii) the exercise group, which was allowed to run voluntarily on running wheels; and (iii) the L-arginine intake group, which was given 2.25% L-arginine solution for 8 weeks from 4 to 12 weeks of age. In the control group, one rat died from stroke and symptoms of stroke were observed in the remaining animals. Similar symptoms were recorded in one rat of the exercise group, but not in the L-arginine group. 3. Blood pressure increased in the control group and this increase was suppressed significantly in the exercise and L-arginine groups. Thrombotic potential in cerebral vessels was the lowest at 4 weeks in all groups and was increased significantly at 12 weeks in the control group, but not in the exercise and L-arginine groups. Plasma concentrations of NO2/NO3 were lower in all animals at 12 weeks compared with those at 4 weeks. This reduction was significantly less marked in the L-arginine group. Cerebral arterioles in control rats at 12 weeks of age were significantly smaller in diameter than those at 4 weeks and these changes were less pronounced in the exercise and L-arginine groups. 4. The results provide clear evidence for the beneficial effects of L-arginine intake and voluntary exercise in mechanisms related to hypertension, thrombosis and stroke.

In vitro and in vivo activities of NS-718, a new lipid nanosphere incorporating amphotericin B, against Aspergillus fumigatus

We evaluated the in vitro and in vivo potencies of a new lipid nanosphere that incorporates amphotericin B (AmB), NS-718, against Aspergillus fumigatus. The in vitro activity of NS-718 (the MIC at which 90% of strains are inhibited [MIC90], 0.25 microgram/ml) against 18 isolates of A. fumigatus was similar to that of deoxycholate AmB (D-AmB; Fungizone; MIC90, 0.25 microgram/ml), but NS-718 was more potent than liposomal AmB (L-AmB; AmBi-some; MIC90, 1.0 microgram/ml). The in vivo efficacy of NS-718 in a rat model of invasive pulmonary aspergillosis was compared with those of D-AmB and L-AmB. A low dose (1 mg/kg of body weight) of L-AmB was ineffective (survival rate, 0%), although equivalent doses of D-AmB and NS-718 were more effective (survival rate, 17%). However, a higher dose of NS-718 (3 mg/kg) was more effective (survival rate, 100%) than equivalent doses of D-AmB and L-AmB (survival rate, 0%). To explain these differences, pharmacokinetic studies showed higher concentrations of AmB in the plasma of rats treated with NS-718 than in the plasma of those treated with D-AmB. Our results suggest that NS-718, a new preparation of AmB, is a promising antifungal agent with activity against pulmonary aspergillosis.

Norepinephrine, but not epinephrine, enhances platelet reactivity and coagulation after exercise in humans

The effects of exercise and catecholamines on platelet reactivity or coagulation and fibrinolysis appear to be inconsistent. This may be partly due to the methods employed in previous studies. In the present study, we investigated the effects of acute aerobic exercise and catecholamines on the thrombotic status by a novel in vitro method, shear-induced hemostatic plug formation (hemostatometry), using nonanticoagulated (native) blood. Aerobic exercise (60% maximal O2 consumption) was performed by healthy male volunteers for 20 min, and the effect on platelet reactivity and coagulation was assessed by performing hemostatometry before and immediately after exercise. Exercise significantly increased shear-induced platelet reactivity, coagulation, and catecholamine levels. The effect of catecholamines on platelet reactivity and coagulation was assessed in vitro by adding catecholamines to blood collected in the resting state. The main findings of the present study are that elevation of circulating norepinephrine at levels that are attained during exercise causes platelet hyperreactivity and a platelet-mediated enhanced coagulation. This may be a mechanism of an association of aerobic exercise with thrombotic risk.

Association between ligand-induced conformational changes of integrin IIbbeta3 and IIbbeta3-mediated intracellular Ca2+ signaling

Platelet IIbbeta3 is a prototypic integrin and plays a critical role in platelet aggregation. Occupancy of IIbbeta3 with multivalent RGD ligands, such as fibrinogen, induces both expression of ligand-induced binding sites (LIBS) and IIbbeta3 clustering, which are thought to be necessary for outside-in signaling. However, the association between LIBS expression and outside-in signaling remains elusive. In this study, we used various IIbbeta3-specific peptidomimetic compounds as a monovalent ligand instead of fibrinogen and examined the association between LIBS expression and outside-in signaling such as IIbbeta3-mediated intracellular Ca2+ signaling. Using a set of monoclonal antibodies (MoAbs) against LIBS, we showed that antagonists can be divided into two groups. In group I, antagonists can induce LIBS on both IIb and beta3 subunits. In group II, antagonists can induce LIBS on the IIb subunit, but not on the beta3 subunit. Inhibition studies suggested that group I and group II antagonists interact with distinct but mutually exclusive sites on IIbbeta3. Neither group I nor group II antagonist increased intracellular Ca2+ concentrations ([Ca2+]i) in nonactivated platelets. All antagonists at nanomolar concentrations abolished the increase in [Ca2+]i in 0.03 U/mL thrombin-stimulated platelets, which is dependent on both fibrinogen-binding to IIbbeta3 and platelet-aggregation. However, only group I antagonists at higher concentrations dose-dependently augmented the [Ca2+]i increase, which is due to aggregation-independent thromboxane A2 production. This increase in [Ca2+]i was not observed in thrombasthenic platelets, which express no detectable IIbbeta3. Thus, only the group I antagonists, albeit a monovalent ligand, can initiate IIbbeta3-mediated intracellular Ca2+ signaling in the presence of thrombin stimulation. Our findings strongly suggest the association between beta3 LIBS expression and IIbbeta3-mediated intracellular Ca2+ signaling in platelets.

Characterization of the binding of FK633 to the platelet fibrinogen receptor

125I-fibrinogen bound to ADP-activated fixed platelets in a saturable manner. The Scatchard plot was curvilinear but nonlinear model fitting of the data suggested that there was only one binding site with KA=4.19+/-1.3 x 10(6) M(-1) and a maximum number of binding sites of 3.9+/-1.1 x 10(4) molecules/platelet. The GPIIb/IIIa antagonists RGDS and FK633 both inhibited 125I-fibrinogen binding (50 microg/ml) in a dose-dependent manner. FK633 had a KB value of 2.5+/-0.48 x 10(7) M(-1) (Kb=39.9 nM) and an IC50, value of 64 nM, while RGDS had an KB of 2.55+/-0.76 x 10(4) M(-1) (Kb=39.2 microM) with an IC50 value of 63 microM. At concentrations below its IC50 value FK633 was a competitive antagonist of fibrinogen binding. However, at concentrations above its IC50 value it was a noncompetitive antagonist. The IC50 values of FK633 remained constant over a wide range of fibrinogen concentrations while its KB value changed-increasing from 1.8+/-0.6 x 10(7) M(-1) at 10 microg/ml 125I-fibrinogen to 4.5+/-1.6 x 10(7) M(-1) at 300 microg/ml and decreasing to 0.3+/-0.2 x 10(7) M(-1) at 2.4 mg/ml. Thus, FK633 is a reversible, noncompetitive antagonist of fibrinogen binding to the platelet GPIIb/IIIa receptor.

Difference of (Ca2+)i movements in platelets stimulated by thrombin and TRAP: the involvement of alpha(IIb)beta3-mediated TXA2 synthesis

This study investigated the difference of [Ca2+]i movement in platelets in response to thrombin and TRAP. The involvement of alpha(IIb)beta3 in this signaling was also studied. Stimulation of platelets with thrombin at 0.03 U/ml caused platelet aggregation and a two-peak increase in [Ca2+]i. The second peak of [Ca2+]i, but not the first peak was abolished by the inhibition of platelet aggregation with alpha(IIb)beta3 antagonists or by scavenging endogenous ADP with apyrase. A cyclooxygenase inhibitor, aspirin, and a TXA2 receptor antagonist, BM 13505, also abolished the second peak of [Ca2+]i but not the first peak, although these regents did not inhibit aggregation. Under the same assay conditions, measurement of TXB2 demonstrated that alpha(IIb)beta3 antagonists and aspirin almost completely inhibited the production of TXB2. In contrast to thrombin-stimulation, TRAP caused only a single peak of [Ca2+]i even in the presence of platelet aggregation, and a high level of [Ca2+]i increase was needed for the induction of platelet aggregation. The inhibition of aggregation with alpha(IIb)beta3 antagonists had no effect on [Ca2+]i change and TXB2 production induced by TRAP. Inhibition studies using anti-GPIb antibodies suggested that GPIb may be involved in the thrombin response, but not in the TRAP. Our findings suggest that low dose thrombin causes a different [Ca2+]i response and TXA2 producing signal from TRAP. Endogenous ADP release and fibrinogen binding to alpha(IIb)beta3 are responsible for the synthesis of TXA2 which results in the induction of the second peak of [Ca2+]i in low thrombin- but not TRAP-stimulated platelets.

Effects of cyclosporine and FK506 on in vitro high shear-induced platelet reactivity in rat and human non-anticoagulated blood

BACKGROUND

The immunosuppressants cyclosporine and FK506 have been used successfully in clinical transplantation, but both agents have various side effects. We have previously found that cyclosporine is prothrombotic and that FK506 is antithrombotic in an in vivo system. The aim of the present study was to assess the effects of these agents on platelet reactivity and coagulation using an in vitro shear-induced hemostatic platelet plug-forming instrument, the hemostatometer.

METHODS

A purpose-built hemostatometer was constructed in our laboratory. The effects of cyclosporine and FK506 on platelet reactivity and coagulation were assessed under high shear stress using non-anticoagulated rat and human blood.

RESULTS

FK506 significantly inhibited both platelet reactivity and coagulation. Cyclosporine also significantly inhibited coagulation, but a proaggregatory effect was observed at a final blood concentration of 0.05 mg/ml.

CONCLUSIONS

The present in vitro results support our previous in vivo findings regarding the prothrombotic and antithrombotic effects of cyclosporine and FK506, respectively.

Comparison of the antithrombotic effects of FK633, GPIIb/IIIa antagonist, and aspirin in a guinea pig thrombosis model

Antiplatelet and antithrombotic effects of FK633 (a GPIIb/IIIa antagonist) and aspirin were compared. FK633 at 0.32 mg/kg i.v. or aspirin at 10 mg/ kg i.v. inhibited ex vivo collagen-induced aggregation by >50% for 1 hour in guinea pigs. However, aspirin was very weak in inhibiting ADP-induced aggregation. In vivo antithrombotic effects of FK633 and aspirin were compared using a FeCl3-induced carotid artery thrombosis model in guinea pigs. Pretreatment with 0.32 mg/kg i.v. of FK633 significantly prevented occlusive thrombus formation, but aspirin at 10 mg/kg i.v. did not. In thrombolysis experiments, adjunctive use of FK633 (0.32 mg/kg i.v.) with rt-PA (0.3 mg/kg bolus+1.0 mg/kg/hr) achieved reperfusion in five of five animals without reocclusion. Aspirin (10O mg/kg i.v.) with rt-PA also achieved reperfusion in three of five animals with high incidence of reocclusion. These results suggest that FK633 may be a more effective antithrombotic agent than aspirin due to its agonist-independent antiplatelet effects.

The differential involvement of von Willebrand factor, fibrinogen and fibronectin in acute experimental thrombosis in rat cerebral and mesenteric microvessels

Arterial thrombi are primarily composed of platelets. Platelets are bound to injured endothelial cells, sub-endothelial matrices, and other platelets by a range of adhesive proteins. Some of these reactions are governed by shear forces. The role of adhesive proteins in the pathogenesis of arterial thrombosis is not fully understood. The aim of this study was to examine the involvement of von Willebrand factor (vWF), fibrinogen (Fg), and fibronectin (FN) in the formation of microvascular thrombi in vivo using a helium-neon laser-induced thrombosis method. Transmission electron microscopy demonstrated that laser irradiation resulted in platelet-rich thrombosis in arterioles and venules, and revealed that this occurred in the absence of endothelial denudation. The mean wall shear rates in mesenteric arterioles and venules were 641 +/- 40 and 280 +/- 20 s-1, respectively. Shear rates increased approximately fivefold in arterioles and tenfold in venules during the formation of occlusive thrombi. Antibody to vWF inhibited thrombosis in arterioles and venules. Antibodies to Fg and FN inhibited thrombosis in venules but not in arterioles. These results confirm that vWF, Fg and FN were involved in thrombogenesis in vivo and demonstrated that significantly higher shear rates were required for the reactions involving vWF than those involving either Fg or FN.

Enhanced thrombogenicity and altered hemodynamics in the cerebral microvasculature of stroke-prone spontaneously hypertensive rats

Thrombotic potential and hemodynamic changes were assessed in the cerebral microcirculation in normal rats (WKY), non-stroke-prone spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP) at the age of 4, 16 and 32 weeks. Whole blood platelet aggregation revealed that the platelet aggregability in vitro was significantly depressed in SHRSP compared to WKY at 16 and 32 weeks using 2 microg/ml collagen but was similar or higher than WKY at 32 weeks using 20 or 40 microg/ml collagen. Platelet-rich thrombi were induced using a helium-neon (He-Ne) laser technique in vivo. The numbers of laser pulses required to induce an occlusive thrombus in arterioles were similar in the three strains at the age of 4 weeks. In contrast, the numbers of laser pulses needed to induce vascular occlusion in SHR (5.5 +/- 0.7; n = 4) and SHRSP (4.9 +/- 0.3; n = 4) were lower than in WKY (7.4 +/- 0.3; n = 5) at the age of 16 weeks. Similar differences were observed at 32 weeks (SHR 5.8 +/- 0.2; n = 6; SHRSP 4.3 +/- 0.1; n = 4; WKY 7.0 +/- 0.2; n = 7). Red blood cell velocities were measured in pial arterioles using a fiber-optic laser Doppler anemometer microscope. Red cell velocities and wall shear rates in SHR and SHRSP were significantly lower than those in WKY (p < 0.05) at the age of 16 weeks and were markedly lower in SHRSP than in either WKY or SHR at the age of 32 weeks. The plasma concentration of nitrite/nitrate determined by the Griess reaction was significantly reduced in SHRSP at 32 weeks compared with 4-week-old rats. These changes could contribute to the enhanced tendency to cerebrovascular stroke in SHRSP.