From Pristine to Heteroatom-Doped Graphene Quantum Dots: An Essential Review and Prospects for Future Research

Graphene quantum dots (GQDs) are carbon-based zero-dimensional materials that have received considerable scientific interest due to their exceptional optical, electrical, and optoelectrical properties. Their unique electronic band structures, influenced by quantum confinement and edge effects, differentiate the physical and optical characteristics of GQDs from other carbon nanostructures. Additionally, GQDs can be synthesized using various top-down and bottom-up approaches, distinguishing them from other carbon nanomaterials. This review discusses recent advancements in GQD research, focusing on their synthesis and functionalization for potential applications. Particularly, various methods for synthesizing functionalized GQDs using different doping routes are comprehensively reviewed. Based on previous reports, current challenges and future directions for GQDs research are discussed in detail herein.

Sandwich-Doping for a Large Schottky Barrier and Long-Term Stability in Graphene/Silicon Schottky Junction Solar Cells

Doping is an effective method for controlling the electrical properties and work function of graphene which can improve the power conversion efficiency of graphene-based Schottky junction solar cells (SJSCs). However, in previous approaches, the stability of chemical doping decreased over time due to the decomposition of dopants on the surface of graphene under ambient conditions. Here, we report an efficient and strong p-doping by simple sandwich doping on both the top and bottom surfaces of graphene. We confirmed that the work function of sandwich-doped graphene increased by 0.61 eV and its sheet resistance decreased by 305.8 Ω/sq, compared to those of the pristine graphene. Therefore, the graphene-silicon SJSCs that used sandwich-doped graphene had a power conversion efficiency of 10.02%, which was 334% higher than that (2.998%) of SJSCs that used pristine graphene. The sandwich-doped graphene-based silicon SJSCs had excellent long-term stability over 45 days without additional encapsulation.

Morphology-Controlled Aluminum-Doped Zinc Oxide Nanofibers for Highly Sensitive NO2 Sensors with Full Recovery at Room Temperature

Room-temperature (RT) gas sensitivity of morphology-controlled free-standing hollow aluminum-doped zinc oxide (AZO) nanofibers for NO2 gas sensors is presented. The free-standing hollow nanofibers are fabricated using a polyvinylpyrrolidone fiber template electrospun on a copper electrode frame followed by radio-frequency sputtering of an AZO thin overlayer and heat treatment at 400 °C to burn off the polymer template. The thickness of the AZO layer is controlled by the deposition time. The gas sensor based on the hollow nanofibers demonstrates fully recoverable n-type RT sensing of low concentrations of NO2 (0.5 ppm). A gas sensor fabricated with Al2O3-filled AZO nanofibers exhibits no gas sensitivity below 75 °C. The gas sensitivity of a sensor is determined by the density of molecules above the minimum energy for adsorption, collision frequency of gas molecules with the surface, and available adsorption sites. Based on finite-difference time-domain simulations, the RT sensitivity of hollow nanofiber sensors is ascribed to the ten times higher collision frequency of NO2 molecules confined inside the fiber compared to the outer surface, as well as twice the surface area of hollow nanofibers compared to the filled ones. This approach might lead to the realization of RT sensitive gas sensors with 1D nanostructures.

Enhanced piezoresponse of highly aligned electrospun poly(vinylidene fluoride) nanofibers

Well-ordered nanostructure arrays with controlled densities can potentially improve material properties; however, their fabrication typically involves the use of complicated processing techniques. In this work, we demonstrate a uniaxial alignment procedure for fabricating poly(vinylidene fluoride) (PVDF) electrospun nanofibers (NFs) by introducing collectors with additional steps. The mechanism of the observed NF alignment, which occurs due to the concentration of lateral electric field lines around collector steps, has been elucidated via finite-difference time-domain simulations. The membranes composed of well-aligned PVDF NFs are characterized by a higher content of the PVDF β-phase, as compared to those manufactured from randomly orientated fibers. The piezoelectric energy harvester, which was fabricated by transferring well-aligned PVDF NFs onto flexible substrates with Ag electrodes attached to both sides, exhibited a 2-fold increase in the output voltage and a 3-fold increase in the output current as compared to the corresponding values obtained for the device manufactured from randomly oriented NFs. The enhanced piezoresponse observed for the aligned PVDF NFs is due to their higher β-phase content, denser structure, smaller effective radius of curvature during bending, greater applied strain, and higher fraction of contributing NFs.

Accuracy of maximal expiratory flow-volume curve curvilinearity and fractional exhaled nitric oxide for detection of children with atopic asthma

Purpose

Airway pathology in children with atopic asthma can be reflected by the concave shape of the maximal expiratory flow-volume (MEFV) curve and high fractional exhaled nitric oxide (FeNO) values. We evaluated the capacity of the curvilinearity of the MEFV curve, FeNO, and their combination to distinguish subjects with atopic asthma from healthy individuals.

Methods

FeNO and angle β, which characterizes the general configuration of the MEFV curve, were determined in 119 steroid-naïve individuals with atopic asthma aged 8 to 16 years, and in 92 age-matched healthy controls. Receiver operating characteristic (ROC) curve analyses were performed to determine the cutoff points of FeNO and angle β that provided the best combination of sensitivity and specificity for asthma detection.

Results

Asthmatic patients had a significantly smaller angle β and higher FeNO compared with healthy controls (both, P<0.001). For asthma detection, the best cutoff values of angle β and FeNO were observed at 189.3° and 22 parts per billion, respectively. The area under the ROC curve for the combination of angle β and FeNO improved to 0.91 (95% confidence interval [CI], 0.87–0.95) from 0.80 (95% CI, 0.75–0.86; P<0.001) for angle β alone and 0.86 (95% CI, 0.82–0.91; P=0.002) for FeNO alone. In addition, the combination enhanced sensitivity with no significant decrease in specificity.

Conclusion

These data suggest that the combined use of the curvilinearity of the MEFV curve and FeNO is a useful tool to differentiate between children with and without atopic asthma.

Negative response elements in keratin genes mediate transcriptional repression and the cross-talk among nuclear receptors

Very little is known about the mechanisms responsible for the findings that binding of nuclear receptors (NR) to some promoter elements leads to transcriptional activation, whereas binding to others leads to repression. Case in point is the group of epidermal keratin genes and their DNA sequences responsible for repression by NR. Keratin response elements (KREs) interact with receptors for retinoic acid, thyroid hormone, and glucocorticoids. KREs, by their structure and sequence, direct the binding of retinoic acid and thyroid hormone as homodimers and glucocorticoids as monomers. Such specific DNA-receptor interactions are crucial for the repression signal of transcription. In this paper we have analyzed the interactions between the KREs and NR that lead to such repression. We have found that KREs are promoter-independent. They not only provide a docking platform for the receptors, but also play a key role in directing the receptors to bind into particular configurations and coordinating the interactions among different receptors. Both an intact KRE and an intact receptor DNA-binding domain are necessary for the regulation to occur, which emphasizes the importance of interaction between the DNA and NR for proper signaling. Furthermore, KREs allow simultaneous binding of multiple receptors, thus providing fine-tuning of transcriptional regulation. The DNA/DNA-binding domain interactions in keratin promoters exemplify tissue and gene specificity of hormone action.

Enzymatic activation associated with programmed fusion of the posterior interfrontal sutures in rats

Fetal rat coronal sutures in culture undergo fusion in the absence of their dura mater. Coinciding with the period of fusion are marked cellular enzymatic changes. Alkaline phosphatase, a marker of osteoblastic activity, and tartrate-resistant acid phosphatase (TRAP), a marker of osteoclastic activity, both increase significantly within fusing sutures and indicate changes in the control of bone synthesis and breakdown. Other enzymes not specifically related to bone formation or degradation also show activation within these fusing sutures. These enzymes include tartrate-sensitive acid phosphatase (TSAP), a marker of lysosomal activity; hexokinase, a glycolytic enzyme; glucose 6-phosphate dehydrogenase (G6PD), an enzyme of the pentose monophosphate shunt; and glutathione reductase, an enzyme of the antioxidant pathway. In the present study, we compared the enzymatic changes previously seen ex vivo with those occurring in vivo during the programmed closure of the posterior interfrontal suture of the rat. This suture fuses between postnatal days 10 and 30 in the rat. The sagittal suture, which remains patent during this period, was used to establish baseline enzymatic activities in a comparable midline suture. Neonatal rats were killed at postnatal days 2, 4, 5, 8, 10, 12, 15, 20, and 30, and posterior interfrontal and sagittal sutures with bone plates on either side were removed. The suture regions of the samples were isolated, dura mater was removed, and suture regions were assayed by microanalytical techniques. Activities of alkaline phosphatase, TRAP, TSAP, hexokinase, G6PD, and glutathione reductase were measured. DNA content was also assayed, and enzyme activities were expressed per amount of DNA. Three pups were killed at each time point, and three to five assays were performed per suture (posterior interfrontal or sagittal) for each time point assayed. Alkaline phosphatase and TRAP activities showed marked increases in fusing sutures compared with nonfusing controls, similar to the increases demonstrated ex vivo. TSAP and hexokinase also showed elevations in the fusing posterior interfrontal sutures, with the greatest differences predominantly during the period of fusion, comparable to the changes seen ex vivo. However, G6PD and glutathione reductase, enzymes of the antioxidant pathway, did not demonstrate the same degree of activation seen ex vivo in fusing sutures. In fact, the levels were actually higher in the patent sagittal samples for the majority of time points examined. Alkaline phosphatase and TRAP activity elevations indicated both osteoblastic and osteoclastic activation during fusion, as seen in the ex vivo phenomenon. TSAP and hexokinase increases also reflected activation in lysosomes and in cellular metabolism during fusion, paralleling the ex vivo situation. However, a less clear pattern of activation in the antioxidant pathway, in contrast to the pattern seen ex vivo, was present. These differences may reflect the different environments of sutures in vivo and ex vivo. Alternatively, oxidative stress may play a more central role in the pathologic process of induced suture fusion ex vivo than in programmed suture fusion in vivo.

Nerve regeneration in diabetic rats

This study evaluated the capacity of diabetic rats to recover the ability to walk after nerve repair or nerve graft of the posterior tibial nerve at thigh level. Functional recovery of the posterior tibial nerve was evaluated by walking track analysis during regeneration in streptozotocin-induced diabetic rats. Surgical procedures were performed 8 weeks after induction of diabetes. The nerve repair was epineurial. The nerve graft was a 1.5 cm segment orthotopically replaced. There was no significant difference in functional recovery between normal and diabetic rats for both the nerve repair and nerve graft groups at 6, 12, and 24 weeks after nerve reconstruction. It is concluded that the presence of diabetes is not a contraindication for nerve reconstruction.

Calreticulin down-regulates both GTP binding and transglutaminase activities of transglutaminase II

Enzyme regulation is an important mechanism for controlling cell proliferation and differentiation in response to extracellular signaling molecules. We have previously reported that a approximately 50 kDa protein (termed Gbetah) consistently copurified with Galphah (transglutaminase II, TGII) and that Gbetah down-regulates the GTPase function of TGII by associating with GDP-bound TGII [Baek et al. (1996) Biochemistry 35, 2651-2657]. In this study, we examined the identity of Gbetah by partial amino acid sequencing and immunological characterizations. The results strongly suggest that Gbetah is a protein known as calreticulin (CRT). When the regulatory role of CRT in the GTPase activity of TGII was examined, CRT inhibited GTP (GTPgammaS) binding and hydrolysis in a concentration-dependent manner. Moreover, CRT interacted only with GDP-bound TGII. These results demonstrate that CRT down-regulates the GTPase activity of TGII by associating with GDP-bound TGII. Studies on the modulation of the TGase activity of TGII revealed that CRT also inhibited TGase activity. The inhibition showed the two characteristics depend on guanine nucleotides occupying the GTPase active site. The inhibition of the "empty" form of the GTPase active site increased the Ca2+ requirement without changing the Vmax. On the other hand, the inhibition of the GDP-bound form decreased Vmax, but did not alter the Ca2+ requirement. Moreover, the GTPgammaS-bound TGII was virtually resistant to Ca2+-mediated stimulation of the TGase activity, indicating that the GTP-bound TGII does not function as a TGase. We concluded that CRT is the regulatory protein of TGII that down-regulates both GTPase and TGase activities, opposing the activators of TGII function.

Cardiac specific overexpression of transglutaminase II (G(h)) results in a unique hypertrophy phenotype independent of phospholipase C activation

Tissue type transglutaminase (TGII, also known as G(h)) has been considered a multifunctional protein, with both transglutaminase and GTPase activity. The role of the latter function, which is proposed as a coupling mechanism between alpha(1)-adrenergic receptors and phospholipase C (PLC), is not well defined. TGII was overexpressed in transgenic mice in a cardiac specific manner to delineated relevant signaling pathways and their consequences in the heart. Cardiac transglutaminase activity in the highest expressing line was approximately 37-fold greater than in nontransgenic lines. However, in vivo signaling to PLC, as assessed by inositol phosphate turnover in [(3)H]myoinositol organ bath atrial preparations, was not increased in the TGII mice at base line or in response to alpha(1)-adrenergic receptor stimulation; nor was protein kinase Calpha (PKCalpha) or PKCepsilon activity enhanced in the TGII transgenic mice. This is in contrast to mice moderately (approximately 5-fold) overexpressing G(alphaq), where inositol phosphate turnover and PKC activity were found to be clearly enhanced. TGII overexpression resulted in a remodeling of the heart with mild hypertrophy, elevated expression of beta-myosin heavy chain and alpha-skeletal actin genes, and diffuse interstitial fibrosis. Resting ventricular function was depressed, but responsiveness to beta-agonist was not impaired. This set of pathophysiologic findings is distinct from that evoked by overexpression of G(alphaq). We conclude that TGII acts in the heart primarily as a transglutaminase, and modulation of this function results in unique pathologic sequelae. Evidence for TGII acting as a G-protein-like transducer of receptor signaling to PLC in the heart is not supported by these studies.

Alpha 1B-adrenoceptor interacts with multiple sites of transglutaminase II: characteristics of the interaction in binding and activation

We previously reported that a novel GTP binding protein (G alpha h) is tissue type transglutaminase (TGII) and transmits the alpha 1B-adrenoceptor (AR) signal to phospholipase C (PLC) through its GTPase function. We have also shown that PLC-delta 1 is the effector in TGII-mediated signaling. In this study, interaction sites on TGII for the alpha 1B-AR were identified using a peptide approach and site-directed mutagenesis, including in vivo reconstitution of TGIIs with the alpha 1B-AR and PLC-delta 1. To identify the interaction sites, 11 synthetic peptides covering approximately 132 amino acid residues of the C-terminal domain of TGII were tested. The studies with the peptides revealed that three peptides, L547-I561, R564-D581, and Q633-E646, disrupted formation of an alpha 1-agonist-alpha 1B-AR-TGII complex and blocked alpha 1B-AR-mediated TGase inhibition in a dose-dependent manner, indicating that these peptide regions are involved in recognition and activation of TGII by the alpha 1B-AR. These three regions were further evaluated with full-length TGIIs by constructing and coexpressing each site-directed mutant with the alpha 1B-AR and PLC-delta 1 in COS-1 cells. Supporting the findings with these peptides, these TGII mutants lost 56-82% the receptor binding ability and reduced by 29-68% the level of alpha 1B-AR-mediated IP3 production via PLC-delta 1 as compared to those with wild-type TGII. The results also revealed that the regions of R564-D581 and Q633-E646 were the high-affinity binding sites of TGII for the receptor and critical for the activation of TGII by the receptor. Taken together, the studies demonstrate that multiple regions of TGII interact with the alpha 1B-AR and that the alpha 1B-AR stimulates PLC-delta 1 via TGII.

Effects of hydroxyethyl-starch-bound deferoxamine on ischemia/reperfusion injury in chronic nerve compression

The authors have demonstrated previously that pretreatment with deferoxamine, an iron chelator and antioxidant, at the time of release in acute nerve compression, provided protection against ischemia/reperfusion (I/R) injury. In the present study, they evaluated whether therapeutic intervention with hydroxyethyl-starch-bound deferoxamine (HES-DFO) at the time of release of the chronically-compressed peripheral nerve protects the nerve from I/R injury. The sciatic nerves of 43 male Sprague-Dawley rats, weighing 325 to 350 g, were subjected to 8 weeks of compression with Silastic tubing. The treatment group received intravenous HES-DFO (70 mg/kg) at the time of decompression, while the control group received an equal volume of intravenous hetastarch vehicle at the same time schedule and route. Nerve-tissue samples from the compression site, as well as contralateral noncompressed nerves, were assayed for malondialdehyde (MDA), a marker of I/R injury. The control group exhibited MDA levels up to five times normal, and did not return to normal for 21 days. In contrast, the HES-DFO group had MDA levels that were not statistically significantly different from normal levels. The results confirm that pretreatment with HES-DFO prior to the surgical decompression of chronically-compressed nerve provides marked protection against I/R injury.

Fixation of the craniofacial skeleton with butyl-2-cyanoacrylate and its effects on histotoxicity and healing

Butyl-2-cyanoacrylate is an easily applied, biocompatible, bioresorbable polymer glue that provides an alternative to conventional rigid fixation techniques. Our aim was to determine if cyanoacrylate fixation of the bone flap in a rabbit craniotomy model provides the healing and strength afforded by plate and screw fixation. We also investigated the inflammatory responses of adjacent tissues including the scalp, cranium, and brain. A unilateral parietal bone flap was elevated in 33 adult New Zealand rabbits. The bone was fixed in position with cyanoacrylate (n = 13), fixed with a microplate and screws (n = 14), or was replaced without fixation (sham-control, n = 6). Normal scar formation and no residual polymer were found in scalp specimens. Neuropathologic analysis identified the presence of residual polymer on the surface of 2 of the 13 rabbit brains. Histopathologic analysis of the bone flap-to-skull interface revealed no difference in the degree but rather in the quality of inflammation and healing between the plate and screw and polymer fixation groups. Microdensitometric analysis of the bone gap revealed nearly equivalent bone density in the cyanoacrylate and plated groups, tending to less density in the sham group (p = 0.11 and 0.09, respectively). An additional study focusing on neurotoxicity was performed in 20 adult rabbits with 3-week and 11-week recovery periods and similarly found the absence of a marked inflammatory response to the polymer. In conclusion, bone healing and soft-tissue inflammation were comparable between cyanoacrylate and plate and screw fixation groups. Although butyl-2-cyanoacrylate glue fixation may provide a reasonable alternative to hardware fixation, further investigations are necessary to identify its ideal utilization.

Role of reactive oxygen species in optic nerve compression injury: a preliminary study

Optic nerve compression is one of the complications in craniofacial surgery and blepharoplasty. We have shown previously that acute and chronic nerve compression produce significant tissue injury in rat sciatic nerve. In the present study the optic nerve was evaluated for possible ischemia/reperfusion injury after acute compression in an animal model. Male New Zealand White rabbits were used in the experiment. The optic nerve was subjected to 2-hour compression followed by reperfusion for 1 hour. Nerve compression was established by banding the optic nerve with silastic tubing. The compressed optic nerve was assayed for malondialdehyde, an indicator of lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS). The TBARS levels increased significantly to 2.5 times normal, from 37+/-6 pmoles per milligram tissue (N=6) to 90+/-12 pmoles per milligram tissue dry weight (N=5) in the compressed/reperfused nerve (p < 0.05). Much of these increases were prevented by treatment with deferoxamine, an iron chelator and antioxidant. The results indicate that optic nerve is injured by acute compression followed by reperfusion. The nerve compression injury appears to be due to reactive oxygen species and can be ameliorated by treatment with free radical scavengers.

Transglutaminase II: a new class of GTP-binding protein with new biological functions

Tissue type transglutaminase (TGase II) is historically a member of the transglutaminase family, which covalently cross-links cellular proteins and polyamines. A recent new finding in the TGase II field is that the enzyme functions as a signal mediator from receptors to an effector in transmembrane signaling. This review will discuss the recent development of TGase II. This new signal transducer was termed Gh when initially discovered and was recently found to be TGase II. To help the reader understand the role of Gh as a signal mediator, the role of heterotrimeric G-proteins in hormone-mediated transmembrane signaling is briefly discussed. We have highlighted how Gh transmits the alpha 1-adrenoceptor signal to the phospholipase C-delta 1 and how Gh is activated and deactivated compared to the prototype of heterotrimeric G-proteins. Recent developments regarding the structure-function of Gh and other biological functions of Gh are discussed to facilitate understanding the impact of Gh in cells.

Osteoblastic and osteoclastic activation in coronal sutures undergoing fusion ex vivo

Numerous studies have demonstrated the importance of dura mater in the normal development and regeneration of the cranium and its sutures. The purpose of this study was to analyze the effect of dura mater on the metabolism of bone during the process of premature suture fusion. Previously, coronal sutures of fetal rats have been shown to fuse in serum-free culture after removal of their dura mater, whereas sutures of neonatal rats resist fusion even without their dura mater present. Sutures from these two distinct developmental stages were evaluated by assaying alkaline phosphatase and tartrate-resistant acid phosphatase (TRAP), marker enzymes of bone synthesis and catabolism, respectively. Coronal sutures with adjacent calvaria were dissected from fetal day 19.5 (F19) rats (n = 142) and neonatal day 1 (N1) rats (n = 42) and randomly divided into two groups each: F19 sutures with dura mater intact; F19 sutures with dura mater removed; N1 sutures with dura mater intact; and N1 sutures with dura mater removed. Calvaria were grown in serum-free medium for up to 21 days, and enzyme activities in suture regions were assayed by microanalytical techniques at different time intervals of culture. F19 sutures without dura mater exhibited significant increases in enzyme activities during days 7 to 21 of culture, whereas those without dura mater did not. N1 sutures with or without dura mater exhibited no significant changes in enzyme activities during the 14-day period of culture. The process of F19 suture fusion, occurring in the absence of dura mater, coincided with the increased activities of both alkaline phosphatase and TRAP. These cellular, enzymatic changes may have implications for the cellular events comprising craniosynostosis in vivo.

Iron-induced rat coronal suture fusion in vitro: the role of redox regulation

The presumptive coronal sutures of rat fetuses at gestation days 19 and 20 have been shown to fuse prematurely when grown in the absence of dura mater in culture. In the present study, the representative enzymes of glucose metabolism and the antioxidative pathway were assayed during the process of suture fusion. The coronal sutures of fetal day 19.5 (F19) and neonatal day 1 rats were grown in the presence or absence of dura mater in serum-free culture. The enzymes assayed were hexokinase (HK) and pyruvate kinase (PK) of glycolysis, and glucose 6-phosphate dehydrogenase (G6PD) and glutathione reductase (GR) of the antioxidative pathway. F19 sutures cultured without dura mater, which fused, showed significant increases in enzyme activities over the preculture levels. HK increased by 200% to 300% of the preculture levels, G6PD by 400% to 500%, GR by 200%, and PK by 400% to 500%. The fetal sutures cultured with dura mater, which did not fuse, showed little alterations of HK, G6PD, and GR activities, but showed a significant 200% to 400% increase in PK activity. Neonatal sutures showed significant increases in enzyme activities during culture, but the presence of dura mater did not significantly affect enzyme activities. High activity levels of enzymes of the antioxidative pathway in F19 sutures coincided with the period of premature suture fusion. Treatment of fetal calvaria with prooxidant (induced by ferrous iron and ascorbic acid) produced suture fusion even in the presence of dura mater. Treatment with deferoxamine (an iron chelator and antioxidant) during the culture prevented suture fusion. The results suggest that fusing sutures experience increased biosynthetic demands and are placed under oxidative stress. When oxidative stress overwhelms the dural influence, the sutures undergo premature fusion.

Alpha 1-adrenergic receptor coupling with Gh in the failing human heart

BACKGROUND

We recently demonstrated that Gh, which transfers the signal from the alpha 1-adrenergic receptor to the 69-kD phospholipase C, is the previously identified tissue-type transglutaminase (TGase II). The alpha 1-adrenergic receptor mediates actions of the sympathetic nervous system, including cardiac, arteriolar, and smooth muscle contractions. In human cardiac tissue, the expression of the alpha 1-adrenergic receptor is increased under pathophysiological conditions, but changes in the physiological response are small. Therefore, it has been suggested that the other components involved in the alpha 1-adrenergic receptor-mediated signaling pathway are probably altered.

METHODS AND RESULTS

Immunological and biochemical studies with nonfailling and failing human heart tissues revealed that the GTP-binding and TGase activities of human heart TGase II (hhG alpha n) are downregulated in both ischemic and dilated cardiomyopathic human heart. In ischemic cardiomyopathy, the alpha 1-adrenergic receptor number increased twofold (27.0 fmol/mg) compared with the nonfailing (12.8 fmol/mg) and the dilated cardiomyopathic (15.6 fmol/mg) heart tissues, but the coupling of hhG alpha h with the alpha 1-adrenergic receptor did not increase. The intrinsic activity of hhG alpha h, was greatly decreased in membrane fractions, whereas the cytosolic TGase activity was not changed. In the dilated cardiomyopathic human heart, these intrinsic enzyme activities of hhG alpha h were also downregulated in the membrane fraction, whereas the amount of hhG alpha h protein was greatly increased (2.8-fold) compared with the nonfailing heart.

CONCLUSIONS

The results of the present study clearly demonstrate that the alpha 1-adrenergic receptor in human heart couples with Gh (TGase II) and indicate that downregulation of hhG alpha h activity is associated with human cardiac failure but that the mechanism differs between ischemic and dilated cardiomyopathies.

Evidence that phospholipase delta1 is the effector in the Gh (transglutaminase II)-mediated signaling

A new class of GTP-binding protein transglutaminase II (Gh) couples to a 69-kDa phospholipase C (PLC). An 8-amino acid region (Leu665-Lys672) of the alpha-subunit of Gh (Galphah) is involved in interaction and activation of PLC, an observation that has now been used to characterize the 69-kDa PLC further. A 20-amino acid peptide corresponding to Leu654-Leu673 of Galphah was used to prepare an affinity resin. On incubation with a partially purified PLC preparation from rat liver membranes, the affinity resin-bound approximately69- and 85-kDa proteins were recognized by an antibody to the 69-kDa PLC. Both purified 69-kDa PLC and PLC-delta1 bound to the affinity resin; moreover, antibodies to PLC-delta1 recognized the 69-kDa PLC, and antibodies to the 69-kDa PLC recognized PLC-delta1. A synthetic peptide corresponding to Leu661-Lys672 of Galphah inhibited the binding of PLC-delta1 to the affinity resin and also stimulated PLC-delta1. Reconstitution of PLC-delta1 with GTPgammaS (guanosine 5'-3-O-(thio)triphosphate)-activated Gh resulted in activation of PLC-delta1. Antibodies to Galphah also coimmunoprecipitated PLC-delta1 upon activation of Gh. These findings indicate that PLC-delta1 is the effector of Gh-mediated signaling.

The effect of cobalt chloride on skin flap survival

The effects of cobalt chloride on ischaemia-reperfusion injury were evaluated in skin flaps. Groin neurovascular island flaps, 3 x 6 cm, were elevated in rats and subjected to primary and secondary ischaemia. Primary ischaemia was produced by 1 hour occlusion of the femoral artery and vein and, 22 hours later, secondary ischaemia was produced by 3 hours venous occlusion. The treatment group received intraperitoneal cobalt chloride (5 or 10 mg/kg) at the time of secondary ischaemia. Flap survival was 80% in the control, 10 to 20% in the cobalt chloride treated, and 20% in the cobalt plus mannitol group. Mannitol (100 mg/kg) failed to prevent the harmful effects of cobalt. Skin flaps exposed to cobalt chloride exhibited increased thiobarbituric acid reactant (TBAR) levels of 20 to 30 times normal. Of the antioxidant enzymes, glutathione peroxidase activity increased by 40% (P < 0.01), whereas glutathione reductase activity decreased by 40% (P < 0.01) in the cobalt exposed groups. Glucose 6-phosphate dehydrogenase activity was not affected.

Oxytocin receptor couples to the 80 kDa Gh alpha family protein in human myometrium

One of the primary functions of the oxytocin receptor is to modulate intracellular calcium levels in myometrium. The oxytocin receptor has been purified and cloned. Although it has been suggested that oxytocin receptor couples with a GTP-binding regulatory protein (G-protein), the identity of this G-protein remains unclear. To elucidate the mechanism of oxytocin receptor signalling, we used the oxytocin-receptor-G-protein ternary complex preparation from human myometrium, and evaluated oxytocin-mediated activation of [35S]guanosine 5'-[gamma-thio]triphosphate ([35S]GTP[S]) binding and [alpha-32P]GTP photoaffinity labelling to a G-protein. Binding of [35S]GTP[S] and the intensity of the [alpha-32P]GTP photoaffinity labelled protein resulting from activation of the oxytocin receptor were significantly attenuated by the selective oxytocin antagonist, desGlyNH2d(CH2)5[Tyr(Me)2,Thr4]OVT. Furthermore, the molecular mass of the specific GTP-binding protein was approximately 80 kDa; homologous with the Gh alpha family, the new class of GTP-binding proteins first identified in rat liver that couples to the alpha 1B-adrenoceptor. Consistent with these observations, in co-immunoprecipitation and co-immunoadsorption of the oxytocin receptor in the ternary complex preparation by anti-Gh7 alpha antibody, the Gh alpha family protein tightly coupled to the oxytocin receptor. These findings demonstrate that oxytocin receptor couples with approximately 80 kDa Gh alpha in signal mediation.

Effects of deferoxamine on ischemia/reperfusion injury after peripheral nerve compression

We have demonstrated previously that acute nerve compression produces ischemia/reperfusion injury in rat sciatic nerve. In this study, we evaluated the effects of deferoxamine, an antioxidant, on recovery from ischemia/reperfusion injury after nerve compression. The sciatic nerves of male Sprague-Dawley rats, 370 to 430 g, were subjected to 24 hours of compression with Silastic tubing. The control group received intravenous saline solution at the time of decompression. The therapeutic group received intravenous deferoxamine (50 mg per kilogram) at the time of removal of the Silastic tubing. Nerve tissues within and distal to the compression site were assayed for malondialdehyde (MDA) levels and for growth-associated protein 43 (GAP-43) expression, as markers of ischemia/reperfusion injury and nerve regeneration, respectively. In the control group (injury alone), the MDA levels were three times higher than normal during the initial 10 days and returned to normal by 14 days. In contrast, the deferoxamine treatment group had MDA levels that were not significantly different from precompression levels. In the control group, enhanced GAP-43 expression persisted until late in the recovery period. In the deferoxamine treatment group, the increased GAP-43 expression subsided early. The results suggest that the treatment of compressed peripheral nerve with deferoxamine at the time of surgical decompression reduces ischemia/reperfusion injury.

A 50 KDa protein modulates guanine nucleotide binding of transglutaminase II

Regulation of cellular response is an important mechanism for controlling cellular functions. The transmembrane signaling of the hormone receptors is regulated by GTP-binding proteins (GTPases) and their associated proteins. Our previous studies demonstrated that the bifunctional GTP-binding protein, G alpha h (transglutaminase II), consistently copurified with an approximately 50 kDa protein (G Beta h) which is dissociated from G alpha h upon activation with GTP gamma S or AlF4-. Present immunological and biochemical studies on the regulation of the GTPase cycle of G alpha h, which involves the alpha 1-adrenoceptor and 50 KDa G beta h, reveal that the 50 kDa protein is indeed a G alpha h-associated protein and down regulates functions of G alpha h. Thus, polyclonal antibody against G Beta h coimmunoprecipitates GDP-bound G alpha h but not the GDP-AlF4--bound form. The GTP gamma S binding and GTPase activity of G alpha h are inhibited in a G beta h concentration dependent manner. Supporting this notion, G beta h accelerated GTP gamma S release from G alpha h and changes the affinity of G alpha h from GTP to GDP. Moreover, the ternary complex preparation exhibits TGase activity that is inhibited in the presence of the alpha 1-agonist and GTP. The GTP gamma S binding by the ternary complex, consisting of the alpha 1-agonist, the receptor, and Gh, is also inhibited by G beta h. The inhibition of GTP gamma S binding with the ternary complex requires a > or = 2.7-fold higher concentration of G beta h than the G alpha h alone, indicating that the receptor enhances the affinity of G alpha h for GTP. In addition, G beta h copurifies with an alpha 1-agonist, adrenoceptor, and G alpha h ternary complex, showing that the complex is a heterotetramer. Our data also suggest that G beta h does not directly interact with alpha 1-adrenoceptor. These findings clearly demonstrate that G alpha h associates with a novel protein which modulates the affinity of G alpha h for guanine nucleotides and that the GDP-bound Gh is the ground state for the counterpart activator, the alpha 1-adrenoceptor, in this signaling system.

Interaction site of GTP binding Gh (transglutaminase II) with phospholipase C

The GTP binding G alpha h (transglutaminase II) mediates the alpha 1B-adrenoreceptor signal to a 69-kDa phospholipase C (PLC). Thus, G alpha h possesses both GTPase and transglutaminase activities with a signal transfer role. The recognition sites of this unique GTP binding protein for either the receptor or the effector are completely unknown. A site on human heart G alpha h (hhG alpha h) has been identified that interacts with and stimulates PLC. Expressed mutants of hhG alpha h with deleted C-terminal regions lost the response to (-)-epinephrine and GTP and failed to coimmunoprecipitate PLC by the specific Gh7 alpha antibody. The interaction regions were further defined by studies with synthetic peptides of hhG alpha h and a chimera in which residues Val665-Lys672 of hhG alpha h were substituted with Ile707-Ser714 residues of human coagulation factor XIIIa. Thus, eight amino acid residues near the C terminus of hhG alpha h are critical for recognition and stimulation of PLC.

Effects of tissue expansion on secondary ischemic tolerance in experimental free flaps

The effects of tissue expansion on free flap tolerance and metabolic response to secondary ischemia were evaluated. A total of 178 male syngeneic Lewis rats were used: 28 in perfusion study and 75 donor and 75 recipient animals in flap survival study. Animals were organized in three experimental groups: control, sham operation, and expansion group. Sham group animals had the expander implanted but not insufflated. After 4 weeks of tissue expansion, 3 x 5-cm epigastric free flaps were transplanted to recipient animals. Twenty-four hours later, secondary ischemia was produced by 3-hour venous occlusion. Flap survival, perfusion, and enzyme activities were determined. Pre-expanded skin flaps had an increase in perfusion of approximately 700% as measured by fluorescein levels compared with control flaps (p < 0.001) and demonstrated a better success rate (76%) compared with those of the control (40%) (p < 0.05) and sham (28%) groups (p < 0.05). Glutathione peroxidase, glutathione reductase, and glucose 6-phosphate dehydrogenase of the antioxidant defense systems significantly increased in skin in both the sham and the expansion groups. In response to secondary ischemia, the control and sham groups exhibited a decrease in enzyme activities of the glutathione redox cycle, whereas the expansion group showed no significant changes from the elevated baseline activities. Tissue expansion improved flap tolerance to secondary ischemia by increasing flap circulation and probably by augmenting tissue metabolic response to oxidative stress.

Free radical damage in acute nerve compression

Nerve compression causes injury by local ischemia and direct mechanical distortion. Peripheral nerves in diabetes mellitus are more prone to injury than those of nondiabetics. We sought to determine whether reperfusion-induced, oxygen-derived free radical injury occurs in peripheral nerves subjected to acute compression in normal and chronically diabetic rats. Female Sprague-Dawley rats weighing 250 to 275 g (N = 347) were divided into two groups: normal and streptozocin-induced diabetics. A total of 187 normal and 160 diabetic nerves were analyzed. After 8 weeks of untreated hyperglycemia, the sciatic nerves of normal and diabetes mellitus rats were subjected to one of three operations: a sham operation, 24-hour compression alone, and 24-hour compression followed by 1-hour reperfusion (CR). Nerve compression was established by banding the right sciatic nerve with a Silastic tubing, 1 cm long and 0.62 mm internal diameter, which was secured with 6-0 nylon suture. In the CR group, after 24 hours of compression, the tubings were released for 1 hour to permit reperfusion. Nerve tissue within the zone of compression underwent biopsy examination and was frozen for subsequent analysis. Blood flow to the nerve was quantified by injecting fluorescein (10 mg/kg intravenously) 10 minutes before harvest and measuring tissue levels fluorometrically. Compression with the Silastic tubing significantly reduced neural blood flow by 75%. Blood flow improved but failed to return to baseline levels after tubing release in diabetes mellitus nerves while perfusion returned to baseline in non-diabetes mellitus nerves. Nerve homogenate was assayed for malonyldialdehyde, an indicator of lipoperoxidation, as well as enzymes of cellular defense and glucose metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 21-aminosteroid U74389F on skin-flap survival after secondary ischemia

The effect of 21-aminosteroid, a lazaroid (U74389F), on tissue injury after secondary ischemia was evaluated in 3 x 5 cm island skin flaps in male Sprague-Dawley rats (n = 30). Primary ischemia was produced by arteriovenous occlusion for 1 hour. Eighteen hours later, secondary ischemia was inflicted by 4-hour venous occlusion. The treatment group received intravenous lazaroid (3 mg/kg) 30 minutes before the start of secondary ischemia. The control group received the same volume of citrate buffer vehicle using the same route and schedule. Skin-flap survival was an all-or-none phenomenon and assessed at 7 days after secondary ischemia. Malondialdehyde (MDA) content was measured to determine the occurrence of lipid peroxidation. Myeloperoxidase (MPO) activity was assayed to assess the degree of neutrophil infiltration. Treatment with this lazaroid significantly improved the survival rate from 0 percent (0 of 13) to 53 percent (9 of 17) (p < 0.01). Malondialdehyde content was 62 +/- 10 (mean +/- SEM, n = 4) pmol/mg dry weight in normal skin. Malondialdehyde increased by 3 times normal in the flaps destined to survive and by 13 times in the flaps destined to undergo necrosis (p < 0.001). Myeloperoxidase activity was negligible in normal skin. At the end of secondary ischemia, the flaps destined to survive exhibited a high myeloperoxidase activity. The flaps destined to necrosis showed the enzyme activity 2.2 times more than surviving flaps (p < 0.01). The results suggest that the lazaroid U74389F may improve survival by attenuating neutrophil infiltration and by reducing lipid peroxidation.

Gh: a GTP-binding protein with transglutaminase activity and receptor signaling function

The alpha 1-adrenergic receptors activate a phospholipase C enzyme by coupling to members of the large molecular size (approximately 74 to 80 kilodaltons) G alpha h family of guanosine triphosphate (GTP)-binding proteins. Rat liver G alpha h is now shown to be a tissue transglutaminase type II (TGase II). The transglutaminase activity of rat liver TGase II expressed in COS-1 cells was inhibited by the nonhydrolyzable GTP analog guanosine 5'-O-(3-thiotriphosphate) or by alpha 1-adrenergic receptor activation. Rat liver TGase II also mediated alpha 1-adrenergic receptor stimulation of phospholipase C activity. Thus, G alpha h represents a new class of GTP-binding proteins that participate in receptor signaling and may be a component of a complex regulatory network in which receptor-stimulated GTP binding switches the function of G alpha h from transglutamination to receptor signaling.

Changes in type VI adenylyl cyclase isoform expression correlate with a decreased capacity for cAMP generation in the aging ventricle

We investigated the developmental regulation of the beta-adrenergic receptor-Gs-adenylyl cyclase pathway in myocardial membranes from fetal, neonatal, adult, and mature adult rats by measuring the density of the beta-adrenergic receptor and the activities of the stimulatory guanine nucleotide-binding protein Gs and the adenylyl cyclase enzyme. Total beta-adrenergic receptor content (in femtomoles per milligram protein) was greatest in the fetal (124.4 +/- 20.5 fmol/mg) and neonatal (122.3 +/- 16.1 fmol/mg) stages and gradually decreased in the adult (90.9 +/- 8.0 fmol/mg) and mature adult (70.0 +/- 9.6 fmol/mg) stages. An equivalent pattern was seen for adenylyl cyclase activity: the basal activity of the effector enzyme or that measured in the presence of 0.1 mmol/L isoproterenol with 0.1 mmol/L Gpp(NH)p, 10 mmol/L NaF, or 0.05 mmol/L forskolin was greater in the fetus and the neonate than in the adult and the mature adult. These data suggested that decreased stimulation of the catalytic unit by Gs could be the underlying cause of diminished adenylyl cyclase activity with aging. However, quantification of Gs by reconstitution into S49 cyc- membranes (in picomoles cAMP per microgram for 10 minutes) demonstrated no significant decrease during development from fetus (1.55 +/- 0.1 pmol/microgram) to neonate (1.9 +/- 0.5 pmol/microgram) and subsequent aging to adult (2.6 +/- 0.2 pmol/micrograms) and mature adult (1.9 +/- 0.2 pmol/microgram). When Northern blot analysis was used to characterize the relative amounts of mRNA coding for Gs alpha, no significant differences were seen among the developmental stages studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of combined cold and hyperbaric oxygen storage on free flap survival

We have previously reported that hyberbaric oxygen (HBO) improved the survival rate of experimental free flaps. The purpose of this study was to evaluate the effects of combined hypothermia and HBO administered during storage on free flaps and on the xanthine oxidase system in rats. Epigastric skin flaps were stored cold for 48 and 72 hours either in room air or under HBO (2.9 atmospheres absolute, 100% oxygen) before free flap transfer. The success rates of free flaps were 80% (8/10) after 48 hours and 20% (2/10) after 72 hours of cold storage in room air. HBO produced no effect after 48 hours but significantly increased the success rate to 70% (7/10) after 72 hours of cold storage. Tissue hypoxanthine (plus xanthine) levels increased to 210% of normal after 48 hours of cold storage in room air and to 176% in HBO. Elevated hypoxanthine levels returned toward normal by 72 hours of cold storage in room air, while the increased levels remained under HBO. Xanthine oxidase activities significantly increased by 60 to 80% during 72 hours of room air storage. HBO treatment inhibited xanthine oxidase activity to 48% of normal by 72 hours of storage. Free flaps exhibited no significant alterations in GR and G6PDH activity after 48 hours of cold storage in room air or HBO. After 72 hours of cold storage, the room air control displayed a trend of decreasing GR activity and a significant 20% decrease in G6PDH activity, while HBO groups showed no significant alterations in both GR and G6PDH activity compared to normal. Protection of the antioxidative enzymes by hypothermia and inhibition of the xanthine oxidase activity by HBO appear to be one of the mechanisms of improved skin flap survival in free flaps.

Flap tolerance to ischaemia in streptozotocin-induced diabetes mellitus

The effects of diabetes mellitus (DM) on skin flap tolerance to 3 h of secondary venous ischaemia were evaluated. Epigastric island flaps were elevated 3, 6 and 12 weeks after induction of DM in rats. In the non-diabetic control groups, the flap survival was 85% in the 3-week group, 72% in the 6-week, and 78% in the 12-week. In untreated DM groups, the flap survival significantly decreased to 40% in the 3-week group, 25% in the 6-week, and 17% in the 12-week (P < 0.05 in all groups). Flap survival in the DM/insulin group decreased to 31% in the 3-week group. Effects of insulin therapy, however, were observed in later stages of DM: 71% and 62% survival in the 6- and 12-week group, respectively. Significant linear correlations between enzymatic responses and the flap survival were found. The results suggest that DM is detrimental to flap tolerance and is associated with the lack of metabolic responses to secondary ischaemia.

Evidence that the Gh protein is a signal mediator from alpha 1-adrenoceptor to a phospholipase C. I. Identification of alpha 1-adrenoceptor-coupled Gh family and purification of Gh7 from bovine heart

Our previous studies on alpha 1-adrenoceptor-mediated signaling suggested that Gh is a signal mediator. Gh consists of a 74-kDa GTP-binding alpha-subunit and a 50-kDa beta-subunit. Studies using the alpha 1-agonist-receptor-G-protein ternary complexes from various tissues and species revealed that the intensity (GTP-binding) of the [alpha-32P]GTP-labeled proteins resulting from activating the alpha 1-receptor was significantly attenuated by phentolamine. The molecular masses of GTP-binding proteins were 74 kDa in rat heart and liver, 77 kDa in dog heart, 78 kDa (Gh7 alpha) in bovine heart and liver, and 80 kDa in human heart. Supporting these observations, a specific antibody to Gh7 alpha not only recognized these GTP-binding proteins in the ternary complex preparations, but also co-immunoprecipitated alpha 1-adrenoceptors, indicating a tight association of these GTP-binding proteins with the alpha 1-adrenoceptor. These results also demonstrate that functional and structural similarities exist among these GTP-binding proteins. Additionally, one of the identified G-proteins (termed Gh7) was purified from bovine heart. Gh7 consisted of the 78-kDa GTP-binding protein and a 50-kDa protein.

Evidence that the Gh protein is a signal mediator from alpha 1-adrenoceptor to a phospholipase C. II. Purification and characterization of a Gh-coupled 69-kDa phospholipase C and reconstitution of alpha 1-adrenoceptor, Gh family, and phospholipase C

Our studies on the alpha 1-adrenoceptor signaling have demonstrated that the Gh family is a signal mediator. We report here that a 69-kDa phospholipase C (PLC) is the effector in this signal pathway. The enzyme was isolated by dissociating a Gh7-PLC complex which was induced in the bovine liver membranes incubating with (-)-epinephrine and GTP. The enzyme displayed a marked preference hydrolysis for phosphatidylinositol 4,5-bisphosphate over other phosphatidylinositides at micromolar calcium. Reconstitution of PLC with the alpha 1-adrenoceptor and Gh (Gh7) into phospholipid vesicles resulted in a lowered Ca2+ requirement for the substrate hydrolysis in the presence of guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) when the receptor was activated with the alpha 1-agonist. The formation of inositol phosphate was hormone concentration dependent and reached maximal within 3 min which was faster than the formation in the presence of the alpha 1-antagonist. An Gh7 alpha antibody co-immunoprecipitated 80-85% of phospholipase C activity in the presence of GTP gamma S, but not in the presence of GDP or buffer, showing the association of PLC with the alpha-subunit of Gh family. Thus, our novel approaches to identify the effector involved in the alpha 1-adrenoceptor signaling, as well as the reconstitution studies, substantially demonstrate that the alpha 1-adrenoceptor-mediated transmembrane signaling involves the Gh family and a 69-kDa PLC.

Microanalyses of enzymes and metabolites in ischemia/reperfusion-induced partial-thickness skin wounds

A transition zone between well-perfused proximal tissue and inadequately perfused distal tissue was evaluated histologically and biochemically in skin flaps. Cranially based pedicle flaps, 3 x 7.5 cm, were made on the backs of female Sprague-Dawley rats. Flap survival was 22% of the original flap area at 7 days and 40% at 14 days after flap elevation (p < 0.001). The transition zone consisted of full-thickness skin survival proximally and partial-thickness wound distally. It is evident that skin wounds induced by ischemia or reperfusion repair continuously between 7 and 14 days after flap elevation. Tissue glucose, lactate, and hypoxanthine levels were measured to assess capillary perfusion in the transition zone on postoperative day 3. The proximal full-thickness skin 5 mm from the wound margin demonstrated no significant changes in glucose and lactate levels compared with normal skin. The partial-thickness wounds exhibited no change in glucose (a 33% decrease was not statistically significant) but a significant increase (319% of normal) in lactate level (p < 0.05). Hypoxanthine levels increased to 453% of normal in full-thickness skin (p < 0.01) and to 787% in partial-thickness wounds (p < 0.001). Metabolic response was evaluated by enzyme assays in the transition zone. Hexokinase activity increased by 251% of normal (p < 0.05), glucose 6-phosphate dehydrogenase by 245% (p < 0.01), and glutathione reductase by 184% (p < 0.05) in the proximal full-thickness skin. Hexokinase activity further increased by 482% of normal (p < 0.01), glucose 6-phosphate dehydrogenase by 379% (p < 0.05), and glutathione reductase by 346% (p < 0.01) in partial-thickness wounds. The results suggest that partial-thickness wounds have less capillary circulation but greater antioxidant enzyme activities than does the survival area with full-thickness skin.

Effects of sympathetic denervation and oxygen free radicals on neovascularization in skin flaps

An island skin flap, with its sole blood supply based on the inferior epigastric vessels, in Sprague-Dawley rats (female, 220 to 250 gm) was used as a model for the investigation of neovascularization. Flap survival after pedicle ligation was considered an indicator of neovascularization. Vascular pedicles were ligated on days 2 to 5 after flap elevation, and the time course of neovascularization in the innervated and denervated flaps was determined by measurements of survival on day 7 after pedicle ligation (on days 9 to 12 postoperatively). Neovascularization sufficient to maintain viability was established at 4 and 5 days after flap elevation in the innervated and denervated flaps, respectively. The effects of various scavengers of oxygen free radicals on neovascularization were evaluated in the innervated and denervated flaps. The pedicles were ligated 3 days after flap elevation. Flap survival was assessed on day 7 after pedicle ligation (on day 10 postoperatively). Treatment with a single dose of deferoxamine (50 mg/kg) increased the viability from 48 to 69 percent of flap area in the denervated flaps (p < 0.01) but produced little effect on viability in the innervated flaps. In the denervated flaps, treatments with a single dose of superoxide dismutase, intravenously and intraarterially, also substantially increased the survival rates from 29 to 86 percent (marginally significant) and 100 percent (p < 0.05), respectively. Allopurinol improved the survival from 43 to 88 percent; the difference was not statistically significant. The results suggest that denervation resulted in a delay of neovascularization and that severe sympathetic denervation contributes to the production of oxygen free radicals, which may exert their inhibitory effects on neovascularization.

Porcine dermal collagen as a wound dressing for skin donor sites and deep partial skin thickness burns

Collagen was extracted by pepsin digestion from porcine skin, and collagen membrane was prepared by salt precipitation. The porcine collagen membrane was evaluated as a burn wound dressing in deep partial skin thickness burn wounds in rats. Burn wounds, 4 x 4 cm, were inflicted by exposure of skin to 75 degrees C for 15 s followed by de-epithelialization. Wound healing was assessed by planimetry of epithelialization on day 10 after injury. Open wounds exhibited 24 per cent of wound area re-epithelialized. Collagen membrane dressing significantly improved the healing to 69 per cent of wound area (P < 0.0001). In a completely separate experiment, the porcine collagen membrane was applied as a wound dressing to the donor sites of burn patients, and its effect on wound healing was compared with that of a petroleum jelly gauze dressing. The donor sites covered with petroleum jelly gauze had re-epithelialized by an average of 14.5 days (ranging from 13 to 16 days) after wounding. The wounds dressed with collagen membrane demonstrated a significant increase in the healing rate. Complete re-epithelialization was observed by 10.3 days (ranging from 10 to 12 days) after wounding (P < 0.0001).

Characterization of a phospholipase C activity regulated by the purified Gh in reconstitution systems

Recently, we have reported that the isolated guanine nucleotide-binding regulatory protein, Gh, couples to the alpha 1-adrenergic receptor (Im, M.-J., and Graham, R. M. (1990) J. Biol. Chem. 265, 18944-18951 and Im, M.-J., Riek, R.P., and Graham, R. M. (1990) J. Biol. Chem. 265, 18952-18960) and has a molecular mass of approximately 74 kDa, and the approximately 50-kDa protein which is copurified probably regulates guanine nucleotide binding of the 74-kDa GTP-binding protein. In this paper, we describe the role of purified Gh in the regulation of phospholipase C in the reconstitution system. The stimulation of phospholipase C activity by Gh effectively occurred at a low calcium concentration (less than or equal to 2 microM), but the phospholipase C (PLC) itself required at least 50-100 times more calcium to become fully activated. The characteristic nature of phospholipase C stimulation by Gh is its response to the calcium concentration. Thus, the enzyme activity changes in narrow submicromolar ranges and reaches maximal stimulation, but it does not extend to the levels above those stimulated by calcium alone. The calcium concentrations for the maximal stimulation of phospholipase C activity were 10-20 microM with phospholipid vesicles and 100-200 microM with detergent solution. These calcium concentrations were further decreased when Gh and phospholipase C were co-reconstituted into the phospholipid vesicles or in the detergent solution. The maximal stimulations of the PLC activity were reached at less than 5 microM calcium in both the vesicles and the detergent solution. The changes of calcium concentration for the activation of PLC are quite different from those obtained by reconstituting PLC-beta 1 with Gq-like G-proteins (Smarcka, A. V., Hepler, J. R., Brown, K. O., and Sternweis, P. C. (1991) Science 251, 804-807 and Taylor, S. J., Chae, H. Z., Rhee, S. G., and Exton, J. H. (1991) Nature 350, 516-518). The phospholipase C activity was stimulated in a Gh concentration-dependent manner in the presence of GTP gamma S. The phospholipase C activity was activated by Gh alpha in the presence of aluminum fluoride, but not by Gh beta. Furthermore, a Gh.PLC complex can be induced by incubation with aluminum fluoride in a detergent solution and partially purified without the dissociation of related proteins. Thus, our reconstitution studies show that the pattern of stimulation of PLC by AIF-4-activated Gh in the ternary complex is similar to the stimulation of PLC activated by Gh in both detergent solution and phospholipid vesicles.

The use of hyperbaric oxygen for preservation of free flaps

The effects of hyperbaric oxygen (HBO) during tissue preservation on flap survival have been investigated in free flaps in rats. Groin skin flaps were harvested, stored in either room air or HBO (100% oxygen at 2.9 atm absolute) at 23 degrees C for 18 hours, and transplanted to the contralateral groin. Free flaps exhibit a high incidence of complete necrosis in the room air control. The survival of free flaps stored under HBO increased from 10% to 60% (p less than 0.05) after 18 hours of preservation. Skin flaps exhibited an increase in tissue hypoxanthine by 3.6-fold normal after 18 hours of storage in room air. HBO preservation prevented the accumulation of hypoxanthine and inhibited xanthine oxidase. Inhibition of the xanthine oxidase system may be one of the mechanisms of improved success of skin flap transplantation.

The effect of bovine basic fibroblast growth factor on skin flap survival in rats

Basic fibroblast growth factor (bFGF) was prepared from bovine pituitary glands and evaluated for its effect on the viability of pedicle skin flaps in rats. Pedicle flaps measuring 3 x 7.5 cm and based cephalad were created on the backs of animals. The treatment group received bFGF in saline solution intradermally by Dermo-jet injection 30 minutes before flap elevation. Skin flaps treated with a single application of 80 U of bFGF demonstrated a significant increase in viability from 40.8% to 69.7% of the flap area (p less than 0.001); the flaps treated with 16 U of bFGF exhibited little improvement. Intradermal administration of bFGF to pedicle skin flaps produced an increase in viability that approximates the increase obtained by a surgical delay procedure; treatment of flaps with exogenous bFGF may offer advantages over surgical delay procedures.

Effects of hyperbaric oxygen preservation on rat limb replantation: a preliminary report

The effect of hyperbaric oxygen, administered during storage, on the survival of replanted limbs was evaluated in rats. The right hindlimbs of male Sprague-Dawley rats were severed and were replanted by microvascular anastomoses after storage in either room air or hyperbaric oxygen (100% oxygen at 2.9 atm absolute) at 23 degrees C for 5 hours. The administration of hyperbaric oxygen during storage improved limb survival from 50% in the room-air, control rats to 100% (p less than 0.05). The gastrocnemius muscle of limbs treated with hyperbaric oxygen demonstrated a higher level of energy reserves (creatine phosphate, adenosine triphosphate, glycogen, and glucose) than the same muscle in room-air, control rats. The mechanisms of the beneficial effect of hyperbaric oxygen on limb survival appears to be related to preservation of high-energy phosphates and glycogen.

Increased survival of island skin flaps by systemic heparin in rats

The effects of systemic heparin on the survival of island skin flaps have been evaluated. Island flaps measuring 3 x 6 cm were created in the abdomen/groin of rats based on an inferior epigastric neurovascular pedicle. The venous drainage from the flap was occluded for various lengths of time ranging from 5 to 10 hours in the control rats and from 8 to 15 hours in the heparin-treated group of rats. The rats in the treated group received 1 ml of heparin solution (300-400 U/kg) through the contralateral saphenous vein immediately prior to the onset venous occlusion and an equivalent dose every 4 hours during venous occlusion. The group of control rats received 1 ml of saline solution. Flap survival was evaluated daily for 7 days. The flaps of control rats demonstrated a gradual decline of the survival rate after 6 hours of venous occlusion and no survival after 10 hours of venous occlusion. The flaps of heparin-treated rats exhibited complete survival until 12 hours of venous occlusion and no survival after 13 hours of venous occlusion. Thus, systemic heparin prolonged tissue tolerance to venous occlusion from 10 to 13 hours. The flaps of control rats demonstrated a significant accumulation of inosine plus hypoxanthine to 260% of normal after 8 hours of venous occlusion. The flaps of heparin-treated rats exhibited little alteration of inosine plus hypoxanthine, and contained a greater concentration of glucose and lactate than the flaps of control rats after 8 hours of venous occlusion. The results demonstrate that systemic heparin can increase tissue tolerance to venous occlusion and improve significantly the flap survival following subsequent reperfusion.

Evidence for an early free radical-mediated reperfusion injury in frostbite

Frostbite is characterized by acute tissue injury induced by freezing and thawing. Initial complete ischemia is followed by reperfusion and later, tissue necrosis. These vascular events support the hypothesis that free radical-mediated reperfusion injury at thawing might contribute to tissue necrosis after frostbite in a manner similar to that seen after normothermic ischemia. To test this hypothesis, rabbit ears were frozen at -21 degrees C for 30, 60, 90, or 120 s and rewarmed at room temperature (22 degrees C). Rabbits were treated "blindly" with saline alone, highly purified, pharmaceutical grade superoxide dismutase (SOD), allopurinol, or deferoxamine. The area of ear necrosis was determined 3 weeks after frostbite by "blinded" morphometry. The administration of SOD at the time of thawing significantly improved viability in ears frozen for 60 and 90 s, but not in those frozen for 30 or 120 s. Deferoxamine also improved viability in ears frozen for 60 s. Allopurinol did not significantly affect ear survival. Electron micrographs showed the appearance of severe endothelial cell injury beginning during freezing and extending through early reperfusion. Later, neutrophil adhesion, erythrocyte aggregation, and microvascular stasis were seen. These findings suggest that free radical-mediated reperfusion injury has a role in frostbite, and quantitate the proportion of the injury that is due to this mechanism.

A novel guanine nucleotide-binding protein coupled to the alpha 1-adrenergic receptor. I. Identification by photolabeling or membrane and ternary complex preparation

The G-protein involved in alpha 1-adrenergic receptor signaling was identified using two different approaches. First, purified rat liver membranes were incubated with [alpha-32P]GTP in the absence or presence of the adrenergic agonist (-)-epinephrine, or in the presence of GTP. After UV irradiation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography, covalent labeling of a number of proteins was apparent and could be blocked by unlabeled GTP. In the preparation treated with (-)-epinephrine alone, labeling of a 74-kDa species was markedly enhanced. Enhanced labeling of 40-50-kDa species was also observed. Labeling of the 74-kDa protein was also evident in similarly treated membranes prepared from FRTL-5 thyroid cells, which contain abundant alpha 1-adrenergic receptors, but not in those prepared from turkey erythrocytes or NIH 3T3 fibroblasts, which are essentially devoid of alpha 1-receptors. Second, alpha 1-agonist-receptor-G-protein ternary complex formation was induced by incubating purified rat liver membranes with (-)-epinephrine. Rauwolscine (10(-7) M) and (+/-)-propranolol (10(-6) M) were included to prevent activation of alpha 2- and beta-adrenergic receptors by (-)-epinephrine. The ternary complex of hormone, receptor, and G-protein was solubilized, partially purified using heparin- and wheat germ agglutinin-agarose, and reconstituted into phospholipid vesicles. The vesicles displayed agonist-stimulated guanosine 5'-O-3-thiotriphosphate (GTP gamma S) binding that was blocked by phentolamine (10(-4) M). By contrast, stimulation of GTP gamma S binding was not evident when the vesicles were incubated with the beta-agonist, isoproterenol. Incubation of the vesicles with [alpha-32P]GTP or [alpha-32P]azido-GTP in the presence of (-)-epinephrine, followed by photolysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography, resulted in the covalent labeling of a 74-kDa protein. Labeling of this protein could be blocked by preincubation with phentolamine or unlabeled GTP. These findings provide direct evidence for the coupling of the alpha 1-adrenergic receptor to a previously uncharacterized G-protein (termed Gh), which has an apparent molecular mass of approximately 74 kDa.

A novel guanine nucleotide-binding protein coupled to the alpha 1-adrenergic receptor. II. Purification, characterization, and reconstitution

In the previous paper, we reported the identification of a 74-kDa G-protein that co-purifies with the alpha 1-adrenergic receptor following ternary complex formation. We report here on the purification and characterization of this 74-kDa G-protein (termed Gh) isolated de novo from rat liver membranes. After solubilization of rat liver membranes with the detergent sucrose monolaurate, Gh was isolated by sequential chromatography using heparin-agarose, Ultrogel AcA 34, hydroxylapatite, and heptylamine-Sepharose columns. The protein, thus isolated, is not a substrate for cholera or pertussis toxin but displays GTPase activity (turnover number, 3-5 min-1) and high-affinity guanosine 5'-O-3-thiotriphosphate (GTP gamma S) binding (half-maximal binding = 0.25-0.3 microM), which is Mg2(+)-dependent and saturable. The relative order of nucleotide binding by Gh is GTP gamma S greater than GTP greater than GDP greater than ITP much much greater than ATP greater than or equal to adenyl-5'-yl imidodiphosphate, which is similar to that observed for other heterotrimeric G-proteins involved in receptor signaling. Moreover, specific alpha 1-agonist-stimulated GTPase (turnover number, 10-15 min-1) and GTP gamma S binding activity could be demonstrated after reconstitution of purified Gh with partially purified alpha 1-adrenergic receptor into phospholipid vesicles. The alpha 1-agonist stimulation of GTP gamma S binding and GTPase activity was inhibited by the alpha-antagonist phentolamine. A 50-kDa protein co-purifies with the 74-kDa G-protein. This protein does not bind guanine nucleotides and may be a subunit (beta-subunit) of Gh. These findings indicate that Gh is a G-protein that functionally couples to the alpha 1-adrenergic receptor.

The effect of a free-radical scavenger, N-2-mercaptopropionylglycine, on the survival of skin flaps

Oxygen free radicals may have an important role in tissue injury, which occurs on reperfusion of previously ischemic skin flaps. Therefore, therapy directed against the toxic effects of reactive oxygen species may protect skin flaps from ischemia/reperfusion injury. Various scavengers of oxygen free radicals have previously been reported to be effective in ameliorating ischemia/reperfusion injury. In the present study, N-2-mercaptopropionylglycine (MPG), a free-radical scavenger, was evaluated for its effectiveness in limiting the extent of necrosis resulting from ischemia/reperfusion injury in rat skin. Island skin flaps were elevated in the abdomen and groin based on an inferior epigastric neurovascular pedicle. The venous drainage from the flap was occluded for 7 hours, and reperfusion was established. The majority of flaps in the control group exhibited complete necrosis on Day 7 postoperatively. Treatment with systemic MPG (20 mg/kg of body weight) significantly improved flap survival from 22 to 71% (p less than 0.01) when administered at the time of reperfusion. However, MPG administered 1 hour after reperfusion did not influence the survival of the flaps. The results suggest that MPG may exert its beneficial effects on flap survival by scavenging oxygen free radicals formed at the time of reperfusion following prolonged ischemia.

The effects of hyperbaric oxygen on free flaps in rats

The effects of hyperbaric oxygen on survival were investigated in free flaps and island flaps. Skin flaps transplanted following 18, 21, and 24 hours of preservation at 24 degrees C demonstrated survival rates of 20%, 10%, and 0%, respectively. Treatment with hyperbaric 100% oxygen improved the survival rates to 66%, 67%, and 40%. A preservation time of 21 to 24 hours at room temperature appears to be the threshold of irreversible ischemic damage. In acute island flaps, flap survival was improved significantly from 35% to 53% and 64% of the random flap area by preoperative or postoperative treatment, respectively. Prolonged preoperative and postoperative treatment improved survival to 66%.

Effect of electrical stimulation on survival of skin flaps in pigs

The purpose of this study was to investigate the effect of electrical stimulation on ischemia-induced tissue injury in skin flaps. Bipedicle skin flaps measuring 4 X 20 cm were created bilaterally on the flanks of 12 Yorkshire pigs. The ischemic central portions of the flaps were treated with 35 mA of electrical current at a frequency of 128 Hz for 30 minutes twice daily during the initial nine days following skin-flap elevation. The treatment schedule consisted of negative-electrode stimulation during the first three days, positive-electrode stimulation during the second three days, and negative-electrode stimulation during the seventh to ninth days. Five control pigs underwent either no treatment (n = 3) or sham treatment (n = 2). The mean area of the skin flaps exhibiting necrosis was 28.0% in the control animals and 13.2% in the stimulated animals. These areas were significantly different (p less than .001). The results indicate that pulsed electrical stimulation can improve the survival of skin flaps.

Improved skin flap survival with nicotinic acid and nicotinamide in rats

The effects of some components of the coenzyme nicotinamide adenine dinucleotide (NAD) on tissue viability were investigated in acute island skin flaps which were constructed to exceed the blood supply provided by a unilateral pedicle of inferior epigastric vessels. Control flaps undergo significant necrosis. Treatment with nicotinamide or nicotinic acid, precursors of NAD, prior to flap elevation significantly improved the area of viability in the random portion of the flap from 44 +/- 9% (mean +/- SD) to 67 +/- 12 and 65 +/- 5%, respectively. Similarly, NAD improved viability to 68 +/- 10% (P less than 0.001). Treatment with other components, adenosine diphosphoribose or quinolinic acid, had no effect on flap survival. The results suggest that nicotinic acid and nicotinamide deserve therapeutic consideration with regard to the treatment of ischemia/reperfusion injury in skin.