The C1 domain of protein kinase C as a lipid bilayer surface sensing module

The activity of membrane-associated protein kinase C (PKC) is tightly controlled by the physical properties of the membrane lipid bilayer, in particular, curvature stress, which is induced by bilayer-destabilizing lipid components. An important example of this is the weakened lipid headgroup interactions induced by phosphatidylethanolamine (PE) and cholesterol. In this work our previous observation with a mixed isoform PKC showing a biphasic dependence of activity as a function of membrane curvature stress [Slater et al. (1994) J. Biol. Chem. 269, 4866-4871] was here extended to individual isoforms. The Ca(2+)-dependent PKCalpha, PKCbeta, and PKCgamma, along with Ca(2+)-independent PKCdelta, but not PKCepsilon or PKCzeta, displayed a biphasic activity as a function of membrane PE content. The fluorescence anisotropy of N-(5-dimethylaminonaphthalene-1-sulfonyl)dioleoylphosphatidylserine (dansyl-PS), which probes the lipid environment of PKC, also followed a biphasic profile as a function of PE content for full-length PKCalpha, PKCbetaIotaIota, and PKCgamma as did the isolated C1 domain of PKCalpha. In addition, the rotational correlation time of both PKCalpha and PKCdelta C1-domain-associated sapintoxin D, a fluorescent phorbol ester, was also a biphasic function of membrane lipid PE content. These results indicate that the C1 domain acts as a sensor of the bilayer surface properties and that its conformational response to these effects may directly underlie the resultant effects on enzyme activity.

Macrophage accumulation associated with rat cardiac allograft rejection detected by magnetic resonance imaging with ultrasmall superparamagnetic iron oxide particles

BACKGROUND

Acute cardiac allograft rejection continues to be the cause of graft loss and contributes to the morbidity and mortality after cardiac transplantation. In this study, we report a new method for detecting organ rejection in transplantation with an MR-based technique using dextran-coated ultrasmall superparamagnetic iron oxide (USPIO) particles. These particles ( approximately 27 nm in diameter) are known to shorten relaxation times in MRI experiments.

METHODS AND RESULTS

A new rat model of heterotopic heart and lung transplantation has been developed for MRI experiments. Allotransplantations (DA-->BN) were performed (n=8), with syngeneic transplantations (BN-->BN) serving as controls (n=8). MR images were obtained with a gradient echo method. At postoperative day 7, allotransplants developed moderate rejection as determined histopathologically. A significant reduction in MR signal intensity was observed after USPIO injection into rats with allotransplanted hearts. Syngeneic transplants showed no differences in MR signal intensity before and after USPIO injections. After injection of USPIO particles at postoperative day 6, a group of allotransplanted rats was treated with cyclosporin A (3 mg/kg). Animals treated with cyclosporin A for 7 days showed no reduction in MR signal intensity after USPIO reinjection at day 14, whereas animals treated for 4 days showed a significant decrease in MR signal intensity in the transplanted hearts indicative of acute graft rejection. Pathological analysis of these animals revealed that dextran-coated USPIO particles were taken up by the infiltrating macrophages that accumulated within the rejecting cardiac graft.

CONCLUSIONS

This MRI method offers promise as a noninvasive method for detecting transplant allograft rejection.

Angiotensin-converting enzyme inhibitor preserves p21 and endothelial nitric oxide synthase expression in monocrotaline-induced pulmonary arterial hypertension in rats

BACKGROUND

Pulmonary arterial hypertension (PAH) is associated with structural changes in the pulmonary vasculature characterized by the proliferation of cellular components of the vessels. ACE inhibitor (ACEI) may have beneficial effects in treating PAH, but its precise mechanism of action in the remodeling process is unclear. p21 is a cyclin-dependent kinase inhibitor that may have a protective role in this process by inhibiting cellular proliferation. Endothelial nitric oxide synthase (eNOS) has also been shown to be protective by its vasodilatory effect. Therefore, we investigated whether expression of p21 and eNOS was modulated by ACEI treatment in a rat model.

METHODS AND RESULTS

Monocrotaline (MCT) was administered to 2 groups of Sprague-Dawley rats fed a high-cholesterol diet, ie, one group received MCT concomitantly with enalapril treatment (MCT(+)/ACEI(+) rats), and the other group did not receive enalapril (MCT(+)/ACEI(-) rats). After 5 weeks, MRI showed right ventricular hypertrophy in MCT(+)/ACEI(-) rats. MCT(+)/ACEI(+) rats showed a preserved right ventricular morphology. Isolated pulmonary perfusion studies showed that ACEI significantly upregulated NO production, as measured by nitrite levels. Addition of N-methyl-D-glucamine dithiocarbamate-Fe solution, an NO-trapping agent, reversed the basal vasodilatory effect of ACEI in the pulmonary vasculature. Immunoblot analysis showed decreased p21 and eNOS expression in the lung in MCT(+)/ACEI(-) rats, whereas their expression was preserved with enalapril treatment.

CONCLUSIONS

ACEI suppresses the development of MCT-induced PAH in rats. The mechanism of action might involve the preservation of p21 and eNOS expression. Both p21 and endothelium-derived NO appear to have protective roles in the development of PAH.

Low- and high-affinity phorbol ester and diglyceride interactions with protein kinase C: 1-O-alkyl-2-acyl-sn-glycerol enhances phorbol ester- and diacylglycerol-induced activity but alone does not induce activity

Phorbol ester-induced conventional protein kinase C (PKCalpha, -betaIota/IotaIota, and -gamma) isozyme activities are potentiated by 1,2-diacyl-sn-glycerol. This has been attributed to a "cooperative" interaction of the two activators with two discrete sites termed the low- and high-affinity phorbol ester binding sites, respectively [Slater, S. J., Milano, S. K., Stagliano, B. A., Gergich, K. J., Ho, C., Mazurek, A., Taddeo, F. J., Kelly, M. B., Yeager, M. D., and Stubbs, C. D. (1999) Biochemistry 38, 3804-3815]. Here, we report that the 1-O-alkyl ether diglyceride, 1-O-hexadecyl-2-acetyl-sn-glycerol (HAG), like its 1,2-diacyl counterpart, 1-oleoyl-2-acetyl-sn-glycerol (OAG), also potentiated PKCalpha, -betaI/II, and -gamma activities induced by the phorbol ester 4beta-12-O-tetradecanoylphorbol-13-acetate (TPA). Similar to OAG, HAG was found to bind to the low-affinity phorbol ester binding site and to enhance high-affinity phorbol ester binding, and to decrease the level of Ca(2+) required for phorbol ester-induced activity, while being without effect on the Ca(2+) dependence of membrane association. Thus, similar to OAG, HAG may also potentiate phorbol ester-induced activity by interacting with the low-affinity phorbol ester binding site, leading to a reduced level of Ca(2+) required for the activating conformational change. However, HAG was found not to behave like a 1,2-diacyl-sn-glycerol in that alone it did not induce PKC activity, and also in that it enhanced OAG-induced activity. The results reveal HAG to be a member of a new class of "nonactivating" compounds that modulate PKC activity by interacting with the low-affinity phorbol ester binding site.

Rehabilitation of persons with central nervous system tumors

A tumor that affects the central nervous system can have a dramatic impact on the individual affected, as well as his or her family and friends. The tumor, regardless of extent or location, may affect the physical, social, vocational, and emotional capabilities of the individual. Basic aspects of rehabilitation for patients with tumors affecting the brain and spinal cord are reviewed in this article. The authors have found that the same principles of neurorehabilitation applied to persons with traumatic brain injury, stroke, and traumatic spinal cord injury are equally appropriate for persons with brain and spinal cord tumors. These principles include the prevention of medical complications; the treatment of medical problems such as pain, spasticity, and neuropathic bowel and bladder; and the improvement of patients' mobility and activities of daily living. Rehabilitation specialists can help prevent complications, maximize function, and improve the quality of life for patients with central nervous system tumors.

Assessment of 2-chloroadenosine treatment after experimental traumatic brain injury in the rat using arterial spin-labeled MRI: a preliminary report

Adenosine is a putative endogenous neuroprotectant. Its action at A1 receptors mitigates excitotoxicity while action at A2 receptors increases cerebral blood flow (CBF). We hypothesized that cerebral injection of the adenosine analog, 2-chloroadenosine, would decrease swelling and increase CBF early after experimental traumatic brain injury (TBI). To test this hypothesis, rats were anesthetized and subjected to TBI using a controlled cortical impact (CCI) model (n = 5/group). Immediately after injury, 2-chloroadenosine (0.3 nmole in 2 microliters) or an equal volume of vehicle were stereotactically injected lateral to the area of contusion. Using magnetic resonance imaging (MRI), in vivo spin-lattice relaxation time of tissue water (Tlobs) and CBF (arterial spin labeling) were measured in a 2-mm thick slice in the injured and non-injured hemispheres at 3-4 h after CCI. In a separate, preliminary experiment, the effect of 2-chloroadenosine injection in normal rat brain was studied. Rats (n = 2) were anesthetized and a burr hole was made for injection of 2-chloroadenosine into the same site as in the TBI model. One rat received the standard dose of 0.3 nmole and one rat received a 6 nmole injection. Tlobs and CBF studies were obtained 1.5-3.5 h after injection, using the same MRI methods as in the TBI study. In rats subjected to TBI, treatment with 2-chloroadenosine attenuated the increase in Tlobs after injury (p < 0.05 for treatment vs vehicle) in both hippocampus and cortex ipsilateral to injury. However, treatment with 2-chloroadenosine did not improve post-traumatic hypoperfusion. In normal rats, injection of 0.3 nmole of 2-chloroadenosine did not increase CBF, but the higher dosage of 6 nmole dramatically increased hemispheric CBF by 1.5-2.0-fold. The effect of local injection of 2-chloroadenosine at a dose of 0.3 nmole after experimental TBI on Tlobs presumably represents a reduction in post-traumatic edema. This reduction in edema, along with the augmentation of CBF seen in normal rats at higher dosage (6 nmole), supports a role for adenosine in neuroprotection following TBI.

Severe traumatic brain injury from unmotorized scooter

The popularity and use of unmotorized, foot-propelled scooters has risen dramatically in the last few years. Increasing reports of traumatic injuries from these scooters have paralleled their commercial sales and success in this country and worldwide. We report a case of a previously healthy 48-year-old woman who suffered a severe traumatic brain injury while riding one of these scooters, resulting in a devastating neurologic outcome and permanent vegetative state. This case emphasizes the importance of public awareness regarding the potential dangers and the need for appropriate precautions and protective gear when riding these recreational devices.

A two-hybrid system for transactivator bait proteins

We describe a two-hybrid strategy for detection of interactions with transactivator proteins. This repressed transactivator (RTA) system employs the N-terminal repression domain of the yeast general repressor TUP1. TUP1-GAL80 fusion proteins, when coexpressed with GAL4, are shown to inhibit transcription of GAL4-dependent reporter genes. This effect requires the C-terminal 30 residues of GAL4, which are required for interaction with GAL80 in vitro. Furthermore, repression of GAL transcription by TUP1-GAL80 requires SRB10, demonstrating that the TUP1 repression domain, in the context of a two-hybrid interaction, functions by the same mechanism as endogenous TUP1. Using this strategy, we demonstrate interactions between the mammalian basic helix-loop-helix proteins MyoD and E12, and between c-Myc and Bin-1. We have also identified interacting clones from a TUP1-cDNA fusion expression library by using GAL4-VP16 as a bait fusion. These results demonstrate that RTA is generally applicable for identifying and characterizing interactions with transactivator proteins in vivo.

Cerebral perfusion during anesthesia with fentanyl, isoflurane, or pentobarbital in normal rats studied by arterial spin-labeled MRI

The influence of anesthetic agents on cerebral blood flow (CBF) was tested in normal rats. CBF is quantified with arterial spin-labeled MRI in rats anesthetized with either an opiate (fentanyl), a potent inhalation anesthetic agent (isoflurane), or a barbiturate (pentobarbital) using doses commonly employed in experimental paradigms. CBF values were found to be about 2.5-3 times lower in most regions analyzed during anesthesia with either fentanyl (with N(2)O/O(2)) or pentobarbital vs. isoflurane (with N(2)O/O(2)), in agreement with findings utilizing invasive measurement techniques. CBF was heterogeneous in rats anesthetized with isoflurane (with N(2)O/O(2)), but relatively homogeneous in rats anesthetized with either fentanyl (with N(2)O/O(2)) or pentobarbital, also in agreement with studies using other techniques. Magn Reson Med 46:202-206, 2001.

Rosuvastatin: do we need another statin?

(1) Rosuvastatin (Crestor(TM)) is a new synthetic agent for the treatment and prevention of lipid disorders, a risk factor for coronary heart disease. (2) Rosuvastatin is undergoing phase III clinical trials. A New Drug Application was submitted to the U.S. Food and Drug Administration in June, 2001. No information on the regulatory status in Canada is currently available. (3) Limited evidence from small clinical trials suggests that rosuvastatin may produce larger dose-dependent decreases in total cholesterol levels and low-density lipoprotein-cholesterol levels in hypercholesterolemic patients compared to other statins. There is insufficient evidence to draw conclusions about the safety of rosuvastatin. (4) The impact of rosuvastatin therapy on cardiac morbidity and mortality is not known. More experience is required to determine the effectiveness and relative benefits of this new drug.

Evaluation of bone mineral density by quantitative ultrasound of bone in 16,862 subjects during routine health examination

Caucasians and Asians are among those with the highest risk for involutional osteoporosis. To obtain accurate data about the prevalence of osteoporosis or osteopenia in different age groups, a large epidemiological study is necessary. Quantitative ultrasound (QUS) of bone is a promising technique in assessing bone microarchitecture in addition to bone mass. This study had two aims. The first was to establish bone mineral density (BMD) using QUS in subjects with no obvious disease undergoing routine health examination. The second was to determine risk factors for osteoporosis in Taiwan in order that better prevention and treatment measures may be provided for these patients. A prospective study of the risk factors for fracture was conducted in the health examination division of Chang Gung Medical Center in Linkou, Taiwan, from January 1996 to December 1997. Broadband ultrasound attenuation of the right heel was measured with an achilles bone densitometer (Lunar, Nauheim, Germany). A total of 16,862 subjects were examined, including 9,314 women (mean age 51.5+/-11.7 years) and 7,548 men (mean age 51.1+/-12.1 years). The incidence of osteoporosis in all subjects increased from 1.13% in the 21--30-year-old age group to 54.55% in those over 80 years of age. 12.02% of the subjects had osteoporosis and 34.45% had osteopenia. From multivariate analysis, bone density evaluated by QUS showed a relationship with age, gender, body mass index, waist/hip ratio, smoking and frequency of exercise. In conclusion, BMD evaluated by QUS is not found to be higher in Taiwan than elsewhere. The role of QUS in predicting fractures in Taiwan requires further investigation.

Characteristics of rodent intestinal mucin Muc3 and alterations in a mouse model of human cystic fibrosis

Human mucin MUC3 and rodent Muc3 are widely assumed to represent secretory mucins expressed in columnar and goblet cells of the intestine. Using a 3'-oligonucleotide probe and in situ hybridization, we observed expression of rat Muc3 mostly in columnar cells. Two antibodies specific for COOH-terminal epitopes of Muc3 localized to apical membranes and cytoplasm of columnar cells. An antibody to the tandem repeat (TR) sequence (TTTPDV)3, however, localized to both columnar and goblet cells. On CsCl gradients, Muc3 appeared in both light- and heavy-density fractions. The lighter species was immunoreactive with all three antibodies, whereas the heavier species reacted only with anti-TR antibody. Thus Muc3 is expressed in two forms, a full-length membrane-associated form found in columnar cells (light density) and a carboxyl-truncated soluble form present in goblet cells (heavy density). In a mouse model of human cystic fibrosis, both soluble Muc3 and goblet cell Muc2 were increased in amount and hypersecreted. Thus Muc2 and Muc3 contribute to the excess intestinal luminal mucus of cystic fibrosis mice.

Subacute cutaneous lupus erythematosus associated with hepatocellular carcinoma

A 63-year-old man with a 4-year history of metastatic hepatocellular carcinoma secondary to chronic hepatitis B developed a rash affecting his arms, legs, thorax and back. Both clinical and histological examination suggested a diagnosis of subacute cutaneous lupus erythematosus (SCLE). The association of SCLE and hepatocellular carcinoma has not previously been reported. The SCLE persisted without remission and was still present at his death from metastatic hepatocellular carcinoma 3 months later. We also review other reported cases of SCLE as paraneoplastic dermatoses and apply McLean's criteria for paraneoplastic dermatosis.

Assessment of the effect of 2-chloroadenosine in normal rat brain using spin-labeled MRI measurement of perfusion

Adenosine analogs such as 2-chloroadenosine are potent cerebrovasodilators. Spin-labeled MRI was used to investigate the spatial distribution, dose-response, and timing of the effect of 2-chloroadenosine on cerebral blood flow (CBF) after intraparenchymal injection into rat brain. Sprague-Dawley rats (N = 10) were injected with 2-chloroadenosine at doses of 0.3, 6.0, or 12 nmoles, or saline vehicle (2-4 microL). CBF was serially quantified in a slice through the injection site in a circular (3.6 mm diameter) region of interest (ROI) around the injection and in ipsilateral hemispheric ROIs at approximately 90 min and approximately 180 min. Marked 3.77- and 3.93-fold increases in CBF (vs. vehicle) were seen in the circular ROI at approximately 90 min and approximately 180 min after 12-nmol injection, respectively. Similarly, 2.92- and 2.78-fold increases in hemispheric CBF were observed at approximately 90 min and approximately 180 min, respectively, after injection of 12 nmoles. Linear dose-response relationships were observed at both times after injection in both ROIs (all P < 0.01). Spin-labeling MRI assessment revealed that parenchymal injection of 2-chloroadenosine produces potent, dose-dependent, and sustained vasodilation over large areas of brain. This treatment and imaging paradigm should facilitate investigation of the effect of CBF promotion in models of traumatic and ischemic brain injury.

Distal ligand reactivity and quaternary structure studies of proximally detached hemoglobins

The linkage between the proximal histidines and the proximal polypeptide in normal adult human hemoglobin (Hb A) has been proposed to play a major role in transmitting allosteric effects between oxygen binding sites [Perutz, M. F. (1970) Nature 228, 726-734]. Here we present circular dichroism (CD), (1)H NMR, analytical ultracentrifugation, and stopped-flow kinetic data to better define the quaternary structure of hemoglobins in which the linkage between the proximal histidines and the polypeptide backbone has been broken [Barrick et al. Nat. Struct. Biol. 4, 78-83 (1997)] and to characterize the distal ligand binding properties of these proximally detached Hbs. CD spectroscopy indicates that rHb (alphaH87G) and rHb (alphaH87G/betaH92G) retain at least partial T-quaternary structure with distal ligand bound, whereas rHb (betaH92G) does not, consistent with (1)H NMR spectra. Analytical ultracentrifugation reveals significant tetramer dissociation in rHb (betaH92G) to be the likely cause of loss of T-state markers. These quaternary structure studies indicate that in distally liganded Hb, the T-state is compatible with proximal linkages in the beta- but not the alpha-chains. (1)H NMR titrations of rHb (alphaH87G) with n-butyl isocyanide demonstrate the alpha-chains to be of high affinity as compared with the beta-chains. Comparing ligand association and dissociation rates between the rHb (alphaH87G) variant with the T- and R-states of wild-type Hb A indicates that at the alpha-chains, carbon monoxide affinity is modulated entirely by the proximal linkage, rather than from distal interactions. Some residual allosteric interactions may remain operative at the beta-chains of rHb (alphaH87G).

Three perspectives of cardiac electrical activity

This article discusses three different perspectives of the electrical activity of the human heart based on three types of electrocardiographic recordings: the Surface ECG, the Subcutaneous ECG, and the Intracardiac Electrogram. Although all three types of recordings are generated by the same electrical activity, namely, the depolarization and repolarization of cardiac cells, the recordings have similarities and differences with regard to method of deployment, duration of implant, duration of recording, maximum long-term storage capacity, signal strength, and susceptibility to electrical noise. The article discusses the similarities and differences among the three types of recordings, as well as the engineering and clinical consequences of these similarities and differences. However, as the consequences include both advantages and disadvantages, the choice of any particular type of recording is eventually dependent on the user.

The stability of cytokeratin 18 in human liver cells during colchicine-induced microtubule disruption

The cytoskeleton plays important roles in cell function and is therefore implicated in the pathogenesis of many human liver diseases, including malignant tumors. The stability of cytokeratin proteins during tumor transformation in human hepatocellular carcinoma has been studied with a molecular approach previously. The results demonstrate that the cytokeratin is modulated in human hepatocellular carcinoma. Besides this, three low molecular weight cytokeratin molecules (named HCC CK) are found. This indicates that these HCC CKs have undergone modulation from the human hepatocyte cytokeratin 18. We also checked the cytokeratin profile of the human hepatoma cell line PLC/PRF/5 with the same methods to ensure the HCC CK molecules are produced by modulation but not protein degradation. The stability of cytokeratin molecules was studied by a different approach. The cytokeratin compositions of human liver cells (Chang cell line) were analysed under the effects of microtubule-disrupting drug (colchicine) by SDS-PAGE, Western blot, immunoprecipitation using a commercially available monoclonal anti-cytokeratin 18 antibody and immunofluorescent staining. Within 1 h of treatment, the microtubule began to collapse and the filamentous structure was shortening. The microtubule had almost collapsed and became fragmented to form a lattice-like network after 24 h of treatment. The cytokeratin was modulated after long-term (24 h) treatment of colchicine, and the molecular weight became 14 kD and the antigenicity was lost. The stability of cytokeratin molecules was related to the intact microtubule network, after disruption of the microtubule the cytokeratin would be modulated. The intact microtubule network was a stabilizing factor of cytokeratin 18 in human liver cells.

Analysis of water vapor content in a ventilator

For medical reasons, a humidifier is sometimes used to add moisture and heat to the air supplied by a ventilator to a patient. However, for a fixed mass of water vapor inside a container, the relative humidity of the air inside the container actually goes down when the temperature of the air is increased, since the saturated vapor pressure of water increases with temperature. Hence, for a type of humidifier that is designed to add only a small amount of water vapor to the patient's air intake, the increase in water vapor due to the humidifier may be hard to substantiate. This article presents one method of verifying that the amount of water in the patient circuit has been increased by the humidifier when the air temperature is also increased. An example will be included to illustrate this method.

An additional H-bond in the alpha 1 beta 2 interface as the structural basis for the low oxygen affinity and high cooperativity of a novel recombinant hemoglobin (beta L105W)

Site-directed mutagenesis has been used to construct three recombinant mutant hemoglobins (rHbs), rHb(beta L105W), rHb(alpha D94A/betaL105W), and rHb(alpha D94A). rHb(beta L105W) is designed to form a new hydrogen bond from beta 105Trp to alpha 94Asp in the alpha(1)beta(2) subunit interface to lower the oxygen binding affinity by stabilizing the deoxy quaternary structure. We have found that rHb(beta L105W) does indeed possess a very low oxygen affinity and maintains normal cooperativity (P(50) = 28.2 mmHg, n(max) = 2.6 in 0.1 M sodium phosphate at pH 7.4) compared to those of Hb A (P(50) = 9.9 mmHg, n(max) = 3.2 at pH 7.4). rHb(alpha D94A/beta L105W) and rHb(alpha D94A) are expressed to provide evidence that rHb(betaL 105W) does form a new H-bond from beta 105Trp to alpha 94Asp in the alpha(1)beta(2) subunit interface of the deoxy quaternary structure. Our multinuclear, multidimensional nuclear magnetic resonance (NMR) studies on (15)N-labeled rHb(beta L105W) have identified the indole nitrogen-attached (1)H resonance of beta 105Trp for rHb(beta L105W). (1)H NMR studies on Hb A and mutant rHbs have been used to investigate the structural basis for the low O(2) affinity of rHb(beta L105W). Our NMR results provide evidence that rHb(beta L105W) forms a new H-bond from beta 105Trp to alpha 94Asp in the alpha(1)beta(2) subunit interface of the deoxy quaternary structure. The NMR results also show that these three rHbs can switch from the R quaternary structure to the T quaternary structure in their ligated state upon addition of an allosteric effector, inositol hexaphosphate. We propose that the low O(2) affinity of rHb(beta L105W) is due to the formation of a new H-bond between alpha 105Trp and alpha 94Asp in the deoxy quaternary structure.

Novel recombinant hemoglobin, rHb (beta N108Q), with low oxygen affinity, high cooperativity, and stability against autoxidation

Using our Escherichia coli expression system, we have constructed rHb (beta N108Q), a new recombinant hemoglobin (rHb), with the amino acid substitution located in the alpha(1)beta(1) subunit interface and in the central cavity of the Hb molecule. rHb (beta N108Q) exhibits low oxygen affinity, high cooperativity, enhanced Bohr effect, and slower rate of autoxidation of the heme iron atoms from the Fe(2+) to the Fe(3+) state than other low-oxygen-affinity rHbs developed in our laboratory, e.g., rHb (alpha V96W) and rHb (alpha V96W, beta N108K). It has been reported by Olson and co-workers [Carver et al. (1992) J. Biol. Chem. 267, 14443-14450; Brantley et al. (1993) J. Biol. Chem. 268, 6995-7010] that the substitution of phenylalanine for leucine at position 29 of myoglobin can inhibit autoxidation in myoglobin and at position 29 of the alpha-chain of hemoglobin can lower NO reaction in both the deoxy and the oxy forms of human normal adult hemoglobin. Hence, we have further introduced this mutation, alpha L29F, into beta N108Q. rHb (alpha L29F, beta N108Q) is stabilized against auto- and NO-induced oxidation as compared to rHb (beta N108Q), but exhibits lower oxygen affinity at pH below 7.4 and good cooperativity as compared to Hb A. Proton nuclear magnetic resonance (NMR) studies show that rHb (beta N108Q) has similar tertiary structure around the heme pockets and quaternary structure in the alpha(1)beta(1) and alpha(1)beta(2) subunit interfaces as compared to those of Hb A. The tertiary structure of rHb (alpha L29F, beta N108Q) as measured by (1)H NMR, especially the alpha-chain heme pocket region (both proximal and distal histidyl residues), is different from that of CO- and deoxy-Hb A, due to the amino acid substitution at alpha L29F. (1)H NMR studies also demonstrate that rHb (beta N108Q) can switch from the R quaternary structure to the T quaternary structure without changing ligation state upon adding an allosteric effector, inositol hexaphosphate, and reducing the temperature. On the basis of its low oxygen affinity, high cooperativity, and stability against autoxidation, rHb (beta N108Q) is considered a potential candidate for the Hb-based oxygen carrier in a blood substitute system.

A novel approach with magnetic resonance imaging used for the detection of lung allograft rejection

OBJECTIVE

Although various techniques have been explored for the detection and quantification of allograft transplant rejection, a practical and reliable method that is noninvasive is still elusive.

METHODS

For our magnetic resonance imaging experiments, we have developed a new rat model of heterotopic lung transplantation to the inguinal region. Allogeneic transplants (DA to Brown Norway) were performed with and without cyclosporine A (INN: ciclosporin) treatment, with syngeneic transplants (Brown Norway to Brown Norway) serving as controls (n = 6 per group). Magnetic resonance images were obtained with a gradient echo method before and after injection of ultra-small superparamagnetic iron oxide particles.

RESULTS

At day 5, allogeneic transplants without cyclosporine A treatment showed a grade 4 rejection histologically. A significantly lower magnetic resonance signal was seen 24 hours after injection of ultra-small superparamagnetic iron oxide particles compared with the preinjection image (346 +/- 7.6 vs 839 +/- 43.4 arbitrary units; P <. 05). Syngeneic transplants showed no evidence of rejection histologically and no differences in magnetic resonance imaging signals between the images before and after injection of ultra-small superparamagnetic iron oxide particles (863 +/- 18.8 vs 880 +/- 22.5). Allotransplants treated with cyclosporine A showed a grade 2 rejection histologically. The change in magnetic resonance signals in that group was small but showed a significant decrease in signal intensity after injection (646 +/- 10.5 vs 889 +/- 23.5, P <.05). Immunohistochemistry and iron staining of the allografts indicated that ultra-small superparamagnetic iron oxide particles were taken up by the infiltrating macrophages that accumulated at the rejection site.

CONCLUSIONS

We have demonstrated a novel approach for the detection of acute lung allograft rejection using magnetic resonance imaging coupled with injection of ultra-small superparamagnetic iron oxide particles. Despite its limitations, our method might be a first step toward a potential clinical application.

NMR reveals hydrogen bonds between oxygen and distal histidines in oxyhemoglobin

Compared with free heme, the proteins hemoglobin (Hb) and myoglobin (Mb) exhibit greatly enhanced affinity for oxygen relative to carbon monoxide. This physiologically vital property has been attributed to either steric hindrance of CO or stabilization of O(2) binding by a hydrogen bond with the distal histidine. We report here the first direct evidence of such a hydrogen bond in both alpha- and beta-chains of oxyhemoglobin, as revealed by heteronuclear NMR spectra of chain-selectively labeled samples. Using these spectra, we have assigned the imidazole ring (1)H and (15)N chemical shifts of the proximal and distal histidines in both carbonmonoxy- and oxy-Hb. Because of their proximity to the heme, these chemical shifts are extremely sensitive to the heme pocket conformation. Comparison of the measured chemical shifts with values predicted from x-ray structures suggests differences between the solution and crystal structures of oxy-Hb. The chemical shift discrepancies could be accounted for by very small displacements of the proximal and distal histidines. This suggests that NMR could be used to obtain very high-resolution heme pocket structures of Hb, Mb, and other heme proteins.

Magnetic resonance imaging detection of rat renal transplant rejection by monitoring macrophage infiltration

BACKGROUND

A rat renal transplantation model was studied by noninvasive magnetic resonance imaging (MRI) with an infusion of ultrasmall superparamagnetic iron oxide (USPIO) particles to test whether the accumulation of immune cells, such as macrophages, could be detected in vivo while the kidney transplant was being rejected.

METHODS

Major histocompatibility disparate DA to BN male rat renal transplantation recipients were infused with USPIO particles, with magnetic resonance (MR) images acquired before, immediately after, and one day following infusion.

RESULTS

When the USPIO infusion was on the fourth day post-transplantation, some rejecting allografts showed a decrease of MR signal intensity one day later. Isografts and allografts with triple immunosuppressant treatment had no MR signal reduction. Immunohistologic staining for ED1+ macrophages and CD4+ and CD8+ T cells in allogeneic transplanted kidneys indicated the accumulation of these immune cells as acute rejection occurred. Morphological studies by electron microscopy confirmed the existence of iron inside the lysosomes of macrophages of rejecting kidneys, while Prussian blue staining detected the presence of iron plaques in macrophages. Isografts and allografts with a triple immunosuppressant treatment exhibited smaller MR signal reductions with minimal histologic changes.

CONCLUSIONS

The concurrence of MR signal reduction following USPIO infusion with pathological manifestation in a rat renal allograft model suggests the possibility that renal transplantation status may be assessed by MRI using USPIO particles as markers for the accumulation of immune cells, such as macrophages.

Serum leptin and vascular risk factors in obstructive sleep apnea

STUDY OBJECTIVES

To define the metabolic profile relevant to vascular risks in obstructive sleep apnea (OSA) and the role of leptin resistance in this risk profile.

DESIGN

Case control study.

SETTING

Sleep Laboratory, Queen Mary Hospital, University of Hong Kong, China.

METHODS

Thirty OSA subjects were matched with 30 non-OSA subjects for body mass index (BMI), age, sex, and menopausal status. Neck, waist, and hip girth, skinfold thickness, and fasting serum levels of lipids, glucose, insulin, and leptin were compared between these two groups.

RESULTS

Compared with control subjects with a similar BMI but without OSA, the OSA group had a significantly more adverse vascular risk factor profile, including dyslipidemia, higher diastolic BP, insulin resistance, and greater adiposity reflected by skinfold thickness. OSA subjects also had higher circulating leptin levels (9.18+/-4.24 ng/mL vs 6.54+/-3.81 ng/mL, mean +/- SD, p = 0.001). Serum leptin levels correlated positively with BMI, skinfold thickness, serum cholesterol, low-density lipoprotein cholesterol, insulin, insulin/glucose ratio, apnea-hypopnea index, and oxygen desaturation time; multiple stepwise regression analysis identified skinfold thickness, waist/hip ratio, serum low-density lipoprotein cholesterol, and diastolic BP as independent correlates, while only serum insulin and diastolic BP were independent correlates in OSA subjects. After treatment with nasal continuous positive airway pressure for 6 months, there was a significant decrease in circulating leptin (p = 0.01) and triglyceride levels (p = 0.02) without change in other parameters.

CONCLUSION

Despite controlling for BMI, OSA subjects showed distinct profiles with clustering of vascular risk factors. Hyperleptinemia was present in the OSA subjects, but it can be normalized by treatment with nasal continuous positive airway pressure, suggesting that increased leptin resistance was not the cause of OSA or its associated vascular risks.