Verotoxin receptor glycolipid in human renal tissue

Infection with verotoxin producing Escherichia coli has been strongly implicated in the etiology of the hemolytic uremic syndrome (HUS). We have previously shown that this toxin specifically binds to a glycolipid receptor-globotriosyl ceramide (Gb3). We have therefore quantitated the level of this glycolipid by HPLC in human renal cortex and medulla as a function of age. We have also measured the binding of verotoxin to Gb3 isolated from each renal tissue sample. Gb3 was a major component of the glycolipid fraction of all renal samples analyzed. The levels were found to be higher in the cortex than medulla, correlating with the clinical incidence of renal lesions in HUS, but reduced in the kidneys of infants as compared to adults. Verotoxin binding was directly proportional to the renal Gb3 content. Thus, human renal tissue is a rich source of the verotoxin receptor glycolipid. However, changes in receptor concentration cannot explain the age-related incidence of HUS.

Production of solid lipid nanoparticle suspensions using supercritical fluid extraction of emulsions (SFEE) for pulmonary delivery using the AERx system

The aims of the current work included: development of a new production method for nanoparticles of water-insoluble drugs in combination with lipids, characterization of the nanoparticles and development of lipid nanosuspension formulations, and investigation of the feasibility of delivering the nanosuspensions as aerosols for inhalation using Aradigm's AERx Single Dose Platform (SDP) with micron-sized nozzles and the all mechanical AERx Essence with sub-micron-sized nozzles. The continuous SFEE method was used for particle precipitation of solid lipid nanoparticles (SLN). The method allowed for production of stable particulate aqueous suspensions of a narrow size distribution, with a volume mean diameter below 30 nm (D99% cumulative volume below 100 nm). Thus the particle size obtained was significantly smaller than previously has been achieved by other techniques. The residual solvent content in the final suspension was consistently below 20 ppm. Drug loading values between 10-20% w/w drug were obtained for model compounds ketoprofen and indomethacin in formulation with lipids such as tripalmitin, tristearin and Gelucire 50/13. It was observed that the loading capacity achieved was higher than the thermodynamic limit of the solubility of the drugs in molten lipids. Lipid nanosuspension formulations were successfully aerosolized using both of the AERx systems. As measured by both cascade impactor and laser diffraction, the aerosol fine particle fraction (FPF) was comparable to drug solution formulations typically used in these devices; i.e., greater than 90% of the aerosol mass resided in particles less than 3.5 mum aerodynamic diameter.

Leg morbidity and function following fibular free flap harvest

Over a period of 3 years, 50 consecutive free fibular flaps for mandibular reconstruction were performed on 47 patients. In 38 patients (81%) a skin paddle was included with the flap to provide either mucosal lining or skin cover; in 9 patients (19%) bone alone was used. Thirty-one patients (66%) required a skin graft to close the donor defect in the leg. Donor leg morbidity and function were determined by patient questionnaire and by physical examination. Forty-one donor sites in 40 patients were available for long-term follow-up. The follow-up ranged from 4 to 39 months with an average of 17 months. Immediate postoperative infection occurred in the donor site of 1 patient (2%) and required additional surgery. There was no other immediate donor site complications when closure required skin grafting. Eleven patients (27%) had late donor site morbidity, consisting of motor weakness of the great toe in 5 patients, ankle instability and/or stiffness in 3 patients, donor site pain in 1 patient, and edema in 2 patients. All complications were graded as mild in severity by the patient and by the examiner. In this series, although most donor site defects required skin grafting, short- and long-term morbidity was minimal. After a short rehabilitation period, all patients were fully able to engage in all daily and recreational activities.

The free vascularised iliac crest tissue transfer: donor site complications associated with eighty-two cases

Seventy-eight patients who had undergone a total of 82 free vascularised iliac crest tissue transfers were reviewed to determine the incidence of donor site complications. The most frequent problems encountered were early postoperative pain and long term sensory changes. Major complications such as femoral neuropathy and incisional hernia formation were encountered infrequently. More serious potential complications are discussed. In general, the functional loss associated with the free vascularised iliac crest tissue transfer was found to be acceptable, but the inclusion of a skin paddle was noted to be associated with a greater incidence of sensory changes, hernia formation and contour abnormalities.

The stability of recombinant human growth hormone in poly(lactic-co-glycolic acid) (PLGA) microspheres

PURPOSE

The development of a sustained release formulation for recombinant human growth hormone (rhGH) as well as other proteins requires that the protein be stable at physiological conditions during its in vivo lifetime. Poly(lactic-co-glycolic acid) (PLGA) microspheres may provide an excellent sustained release formulation for proteins, if protein stability can be maintained.

METHODS

rhGH was encapsulated in PLGA microspheres using a double emulsion process. Protein released from the microspheres was assessed by several chromatrographic assays, circular dichroism, and a cell-based bioassay. The rates of aggregation, oxidation, diketopiperazine formation, and deamidation were then determined for rhGH released from PLGA microspheres and rhGH in solution (control) during incubation in isotonic buffer, pH 7.4 and 37 degrees C.

RESULTS

rhGH PLGA formulations were produced with a low initial burst (< 20%) and a continuous release of rhGH for 30 days. rhGH was released initially from PLGA microspheres in its native form as measured by several assays. In isotonic buffer, pH 7.4 and 37 degrees C, the rates of rhGH oxidation, diketopiperazine formation, and deamidation in the PLGA microspheres were equivalent to the rhGH in solution, but aggregation (dimer formation) occurred at a slightly faster rate for protein released from the PLGA microspheres. This difference in aggregation rate was likely due to the high protein concentration used in the encapsulation process. The rhGH released was biologically active throughout the incubation at these conditions which are equivalent to physiological ionic strength and pH.

CONCLUSIONS

rhGH was successfully encapsulated and released in its fully bioactive form from PLGA microspheres over 30 days. The chemical degradation rates of rhGH were not affected by the PLGA microspheres, indicating that the internal environment of the microspheres was similar to the bulk solution. After administration, the microspheres should become fully hydrated in the subcutaneous space and should experience similar isotonic conditions and pH. Therefore, if a protein formulation provides stability in isotonic buffer, pH 7.4 and 37 degrees C, it should allow for a safe and efficacious sustained release dosage form in PLGA microspheres.

Shiga toxin-associated hemolytic uremic syndrome: interleukin-1 beta enhancement of Shiga toxin cytotoxicity toward human vascular endothelial cells in vitro

Development of hemolytic uremic syndrome (HUS) after infection by Shigella dysenteriae 1 or enterohemorrhagic Escherichia coli has been associated with the production of Shiga toxins (verotoxins). The putative target of Shiga toxins in HUS is the renal microvascular endothelium. This report shows that preincubation of human umbilical vein endothelial cells (HUVEC) with interleukin-1 beta (IL-1 beta) enhances the cytotoxic potency of Shiga toxin toward HUVEC. A preincubation of HUVEC with IL-1 beta is required for sensitization of HUVEC to Shiga toxin. Sensitization of HUVEC to Shiga toxin is IL-1 beta dose dependent. Development of the IL-1 beta response is time dependent, beginning within 2 h of IL-1 beta preincubation and increasing over the next 24 h. That these responses were due to IL-1 beta was demonstrated by heat inactivation of IL-1 beta, by neutralization of IL-1 beta by specific antibody, and by the ability of an IL-1 beta receptor antagonist to inhibit the effect of IL-1 beta. Shiga toxin-related inhibition of HUVEC protein synthesis preceded loss of cell viability. IL-1 beta incubation with HUVEC induced the receptor for Shiga toxin, globotriaosylceramide. Lipopolysaccharide included during IL-1 beta preincubation with HUVEC increased sensitivity to Shiga toxin in an additive manner. We conclude that IL-1 beta may induce Shiga toxin sensitivity in endothelial cells and contribute to the development of HUS.

De Novo Pathogenic Variants in CACNA1E Cause Developmental and Epileptic Encephalopathy with Contractures, Macrocephaly, and Dyskinesias

Developmental and epileptic encephalopathies (DEEs) are severe neurodevelopmental disorders often beginning in infancy or early childhood that are characterized by intractable seizures, abundant epileptiform activity on EEG, and developmental impairment or regression. CACNA1E is highly expressed in the central nervous system and encodes the α₁-subunit of the voltage-gated Ca_V2.3 channel, which conducts high voltage-activated R-type calcium currents that initiate synaptic transmission. Using next-generation sequencing techniques, we identified de novo CACNA1E variants in 30 individuals with DEE, characterized by refractory infantile-onset seizures, severe hypotonia, and profound developmental impairment, often with congenital contractures, macrocephaly, hyperkinetic movement disorders, and early death. Most of the 14, partially recurring, variants cluster within the cytoplasmic ends of all four S6 segments, which form the presumed Ca_V2.3 channel activation gate. Functional analysis of several S6 variants revealed consistent gain-of-function effects comprising facilitated voltage-dependent activation and slowed inactivation. Another variant located in the domain II S4-S5 linker results in facilitated activation and increased current density. Five participants achieved seizure freedom on the anti-epileptic drug topiramate, which blocks R-type calcium channels. We establish pathogenic variants in CACNA1E as a cause of DEEs and suggest facilitated R-type calcium currents as a disease mechanism for human epilepsy and developmental disorders.

Lipid modulation of glycolipid receptor function. Availability of Gal(alpha 1-4)Gal disaccharide for verotoxin binding in natural and synthetic glycolipids

Verotoxins bind to glycosphingolipids containing terminal Gal(alpha 1-4)Gal residues. Globotriaosylceramide is the most effective receptor for verotoxin-1 in vitro and is the functional plasma-membrane receptor which mediates cytopathology for most sensitive cells. Binding of verotoxin-1 to a series of galabiose-containing or globotriaose-containing synthetic glycolipids with monoalkylsulfides and bisalkylsulfides or sulfones as the lipid moiety, have been studied for toxin binding by TLC overlay and in solid phase in the presence of auxiliary lipids. The results demonstrate that for an identical carbohydrate, binding is dramatically altered according to the nature of the lipid moiety. The close proximity of the galabiose sequence and the hydrophobic species also compromised recognition. The lipid environment is also a major determinant of receptor function, since species that were effective, even preferred toxin receptors as monitored by TLC overlay, were not necessarily recognized in the presence of auxiliary lipids. Certain glycolipids, which were not recognized by TLC overlay, were nevertheless found to be effective receptors in an auxiliary lipid matrix. These results demonstrate the crucial role of the lipid moiety in verotoxin/glycolipid recognition and are discussed in relation to toxin pathogenesis and glycolipid receptor function.

Alteration of the glycolipid binding specificity of the pig edema toxin from globotetraosyl to globotriaosyl ceramide alters in vivo tissue targetting and results in a verotoxin 1-like disease in pigs

All members of the verotoxin (VT) family specifically recognize globo-series glycolipids on the surface of susceptible cells. Those toxins that are associated with human disease, VT1, VT2, and VT2c, bind to globotriaosyl ceramide (Gb3) while VT2e, which is associated with edema disease of swine, binds preferentially to globotetraosyl ceramide (Gb4). We were recently able to identify, using site-directed mutagenesis, amino acids in the binding subunit of these toxins that are important in defining their glycosphingolipid (GSL) binding specificity (Tyrrell, G. J., K. Ramotar, B. Boyd, B. W. Toye, C. A. Lingwood, and J. L. Brunton. 1992. Proc. Natl. Acad. Sci. USA. 89:524). The concomitant mutation of Gln64 and Lys66 in the VT2e binding subunit to the corresponding residues (Glu and Gln, respectively) found in VT2 effectively converted the GSL binding specificity of the mutant toxin from Gb4 to Gb3 in vitro. We now report that the altered carbohydrate recognition of the mutant toxin (termed GT3) has biological significance, resulting in a unique disease after intravascular injection into pigs as compared with classical VT2e-induced edema disease. The tissue localization of radiolabeled GT3 after intravascular injection was elevated in neural tissues compared with VT2e accumulation, while localization of GT3 to the gastrointestinal tract was relatively reduced. Accordingly, the pathological lesions after challenge with GT3 involved gross edema of the cerebrum, cerebellum, and brain stem, while purified VT2e caused hemorrhage and edema of the cerebellum, and submucosa of the stomach and large intestine. In addition, both radiolabeled toxins bound extensively to tissues not directly involved in the pathology of disease. VT2e, unlike GT3 or VT1, bound extensively to red cells, which have high levels of Gb4. The overall tissue distribution of VT2e was thus found to be influenced by regional blood flow to each organ and not solely by the Gb4 levels of these tissues. Conversely, the distribution of GT3 (and VT1), which cleared more rapidly from the circulation, correlated with respective tissue Gb3 levels rather than blood flow. These studies indicate the primary role of carbohydrate binding specificity in determining systemic pathology, suggest that the red cells act as a toxin carrier in edema disease, and indicate that red cell binding does not protect against the pathology of systemic verotoxemia.

Alteration of the carbohydrate binding specificity of verotoxins from Gal alpha 1-4Gal to GalNAc beta 1-3Gal alpha 1-4Gal and vice versa by site-directed mutagenesis of the binding subunit

Verotoxin 1 (VT-1) and Shiga-like toxin II (SLT-II) bind to the glycosphingolipid (GSL), globotriaosylceramide (Gb3), whereas pig edema disease toxin (VTE) binds to globotetraosylceramide (Gb4) and to a lesser degree Gb3. Amino acids important in the GSL binding specificity of VT-1 and VTE have been identified by site-directed mutagenesis. One mutation, Asp-18----Asn, in VT-1 resulted in binding to Gb4 in addition to Gb3 in a manner similar to VTE. Several mutations in VTE resulted in the complete loss of GSL binding; however, one mutation resulted in a change in the GSL binding specificity of the VTE B subunit. The double mutation Gln-64----Glu and Lys-66----Gln (designated GT3) caused a selective loss of Gb4 binding, effectively changing the binding phenotype from VTE to VT-1. Both wild-type VTE and GT3 were purified to homogeneity and binding kinetics in vitro were determined with purified GSLs from human kidney. The cell cytotoxicity spectrum of the mutant toxin was also found to be altered in comparison with VTE. These changes were consistent with the GSL content of the target cells.

Characterization of Shiga-like toxin I B subunit purified from overproducing clones of the SLT-I B cistron

The cistron encoding the B subunit of Escherichia coli Shiga-like toxin I (SLT-I) was cloned under control of the tac promoter in the expression vector pKK223-3 and the SLT-I B subunit was expressed constitutively in a wild-type background and inducibly in a lacIq background. The B subunit was located in the periplasmic space, and less than 10% was found in the culture medium after 24 h incubation. Polymyxin B extracts contained as much as 160 micrograms of B subunit/ml of culture. B subunit was purified to homogeneity by ion-exchange chromatography followed by chromatofocusing. Cross-linking analysis of purified native B subunit showed that it exists as a pentamer. In gels containing 0.1% SDS the native protein dissociated into monomers. B subunit was found to have the same glycolipid-receptor-specificity as SLT-I holotoxin. Competitive binding studies showed that B subunit and holotoxin had the same affinity for the globotriosylceramide receptor. We conclude that this recombinant plasmid is a convenient source of large amounts of purified SLT-I B subunit, which could be used for biophysical and structural studies or as a natural toxoid.

Acute ischaemic preconditioning protects against skeletal muscle infarction in the pig

OBJECTIVE

The aims were to investigate the efficacy of acute ischaemic preconditioning for protection of skeletal muscles against infarction and its effect on muscle blood flow and ischaemic muscle metabolism.

METHODS

The efficacy of preconditioning was tested by subjecting pig latissimus dorsi and gracilis muscles to different numbers and durations of ischaemia/reperfusion cycles before 4 h of global ischaemia. Infarction was assessed at 48 h of reperfusion, using nitroblue tetrazolium dye. Blood flow in the latissimus dorsi was measured at the end of preconditioning and 1.5 and 3.0 h of reperfusion, using the radioactive microsphere (15 microns) technique. Muscle biopsies were taken from the latissimus dorsi before ischaemia, at the end of 2 and 4 h of ischaemia, and 1.5 h of reperfusion.

RESULTS

At least three cycles of 10 min ischaemia and 10 min reperfusion were required for preconditioning of latissimus dorsi and gracilis muscles for protection against infarction. Preconditioning reduced the total infarct size by 44% and 62% in latissimus dorsi and gracilis muscles, respectively. Preconditioning did not affect preischaemia muscle blood flow but it reduced the muscle content (preischaemia reserve) of phosphocreatine and ATP and the muscle energy charge potential (ECP) by 13.5%*, 27.5%*, and 8%* (*P < 0.05), respectively. In spite of a lower preischaemia reserve of phosphocreatine and ATP, the muscle contents of phosphocreatine and ATP and muscle ECP were maintained higher and the lactate lower (*P < or = 0.05) in the preconditioned than in the non-preconditioned (control) muscles at the end of 4 h of ischaemia [phosphocreatine 8.0(SEM 0.4) v 3.2(0.3)*; ATP 9.8(0.7) v 7.8(0.3); ECP 0.72(0.02) v 0.66(0.01)*; lactate 115.4(8.6) v 160.5(11.8)* mumol.g-1 dry muscle]. The level of ATP and ECP also remained significantly higher and the level of lactate significantly lower in the preconditioned than in the non-preconditioned latissimus dorsi muscles at 1.5 h of reperfusion. Hyperaemia was seen in the preconditioned latissimus dorsi muscles at 1.5 h of reperfusion and it subsided by the end of 3h of reperfusion.

CONCLUSIONS

The protective effect of preconditioning can be induced in pig skeletal muscle but at a higher threshold than reported previously in pig cardiac muscle (one cycle). Preconditioning of pig skeletal muscle is associated with a lower energy metabolism during sustained ischaemia. At the present time, it is not known if this energy sparing effect is a major mechanism of ischaemic preconditioning against infarction in skeletal muscles.

Evidence that verotoxins (Shiga-like toxins) from Escherichia coli bind to P blood group antigens of human erythrocytes in vitro

The interaction of verotoxins (VTs) with human erythrocytes (RBCs) in vitro was investigated, with particular reference to the role of P blood group glycolipids that are structurally related to the known VT receptors. RBC binding of purified VT1, VT2, VT2c, and VT2e was detected by direct and indirect immunofluorescence. Glycolipids were extracted from defined RBCs, separated by thin-layer chromatography, and assessed for VT binding in an overlay assay by adding toxin and specific antibodies. All VTs bound to P1 phenotype (Pk, P, and P1 antigens) and P2 phenotype (Pk and P antigens) RBCs but not to p phenotype (lacking the Pk, P, and P1 antigens) RBCs. Binding of VT1 and VT2 was approximately 10-fold greater to P1 and the rare Pk2 (Pk antigen but no P1 or P antigen) phenotype cells than to P2 phenotype RBCs, whereas VT2e bound equally well to P1 and P2 phenotype cells. The VT1 and VT2 immunofluorescence results correlated with the detection of P1 and/or increased amounts of Pk (globotriaosylceramide) antigen; VT2e immunofluorescence correlated with the detection of P (globotetraosylceramide) antigen. The Pk band pattern and VT binding observed in the thin-layer chromatogram of human P1 and P phenotype RBC extracts varied from that of human kidney and Pk1 phenotype (Pk and P1 antigens) RBCs. We conclude that each VT binds to human RBCs in vitro by utilizing specific P blood group glycolipids as receptors. On P1 and P phenotype RBCs, the accessibility of the Pk antigen for VTs appeared to be restricted. The occurrence of VT-RBC binding in natural VT-producing Escherichia coli disease and its relevance for the pathophysiology of hemolytic uremic syndrome remain to be established.

Identification of the key protein for zinc uptake in Hemophilus influenzae

Very little is known about specific mechanisms for zinc accumulation and transport in bacteria. In this study a putative adhesin B in Hemophilus influenzae, the product of gene HI0119, has been identified as a periplasmic zinc-binding protein (PZP1). A pzp1-deficient mutant has been constructed which is defective for growth under aerobic conditions and grows poorly under anaerobic conditions. The growth defect is specifically rescued by supplementing the growth medium with high concentrations of zinc. Subcellular fractionation was used to localize PZP1 to the periplasmic region in a nontypeable H. influenzae strain and in a transfected recombinant Escherichia coli strain (TApzp1). Recombinant PZP1, purified from a periplasmic extract of E. coli strain TApzp1, contained approximately two zinc atoms/protein molecule as determined by neutron activation analysis and atomic absorption spectroscopy. The zinc atoms could be removed by incubation with EDTA, and, by further addition of zinc, a total of five zinc atoms/PZP1 could be bound. Direct binding of 65Zn to the recombinant protein by Western blot was demonstrated. Taken together, these results provide direct evidence that PZP1 plays a key role in zinc uptake by H. influenzae.

A comparison of the effects of verocytotoxin-1 on primary human renal cell cultures

Infection with verocytotoxin-producing Escherichia coli causes haemolytic uraemic syndrome (HUS). Verocytotoxin-1 (VT1) is cytopathic to renal microvascular endothelial cells in culture, supporting the hypothesis that the vasculopathy of HUS is caused directly by the toxic action of VT1 on cells. We provide evidence that VT1 inhibits protein synthesis in primary cultures of glomerular epithelial cells (GE), cortical tubular epithelial cells (CTE) and mesangial cells (MC). Using 100 pg/ml of VT1 we saw a decrease in protein synthesis to 14.3+/-1.9% in vero cells (a primate cell line), 1.7+/-0.3% in GE, 0.9+/-0.4% in CTE and 74.8+/-1.3% in MC at 24 h. The human renal epithelial cells are at least as sensitive as vero cells to the protein synthesis inhibitory effects of VT1 if not more so. Cell viability decreased in all cultures as measured by MTT reduction, neutral red incorporation and lactate dehydrogenase release and followed the same pattern of susceptibility as for protein synthesis inhibition. However, unlike vero cells, death occurred without DNA fragmentation. Cell sensitivity was greatest in cells which bound more VT1.

A comparison of the results following oromandibular reconstruction using a radial forearm flap with either radial bone or a reconstruction plate

Fifteen cases of oromandibular reconstruction using a radial osteocutaneous flap were compared with 16 in which the mandible was replaced with a reconstruction plate and a forearm flap was used for intraoral lining. All cases involved oral cancer; most had been irradiated. Nine survived in each group. Complications included one infected nonunion in addition to two bone exposures in the bone group, compared with three cases of plate exposure and two bone exposures in the plate group. Functional results were similar in both, but osteointegrated implants were possible only in the patients receiving bone. Cosmesis seemed somewhat better in the plate group. Donor-site problems were common but minor, and long-term forearm function was slightly reduced in both groups. Although the sample sizes were small, the reconstruction plate together with a radial forearm flap appeared to provide effective reconstruction following composite resection. However, we would not recommend this for the younger patient or in benign disease.

Verotoxins inhibit the growth of and induce apoptosis in human astrocytoma cells

Verotoxin 1 (VT1) is an E. coli toxin comprising an A subunit with N-glycanase activity, and five smaller B subunits capable of binding to the functional receptor globotriaosylceramide (Galalpha1-4-Galbeta1-4-Glcceramide-Gb3). VT is implicated in hemorrhagic colitis and the more serious hemolytic uremic syndrome. VT1 is active against various tumor cell lines in vitro and in vivo. To extend the anti-cancer spectrum of activity of VT to human brain tumors, in the present analysis we studied the effects of VT on the growth of 6 permanent human astrocytoma cell lines. All astrocytoma cell lines analyzed express Gb3 and were sensitive to VT-1 at a dose of 50 ng/ml, but sensitivity was not proportional to the relative Gb3 concentration. VT induced apoptosis in these cells was shown by electron microscopy. Morphological evidence (nuclear shrinkage and chromatin condensation) of apoptosis could be clearly distinguished 1.5 hrs after toxin addition. Ultrastructural preservation of organelles was observed in conjunction with blebbing of the plasma membrane, condensation of chromatin within the nucleus and nuclear shrinkage. Apoptosis was also induced by the recombinant toxin B subunit alone, suggesting that the ligation of Gb3 is the primary induction mechanism. These studies indicate that verotoxin/Gb3 targetting may provide a novel basis for the inhibition of astrocytoma tumour cell growth.

Shiga toxin-associated hemolytic uremic syndrome: effect of sodium butyrate on sensitivity of human umbilical vein endothelial cells to Shiga toxin

Escherichia coli O157:H7-related vascular damage such as hemolytic uremic syndrome is believed to require the Shiga-like toxins. This study demonstrated that sodium butyrate sensitized human umbilical vein endothelial cells to Shiga toxin and increased the expression of Shiga toxin receptor, globotriaosylceramide (Gb3), on human umbilical vein endothelial cells.

Serological responses to the B subunit of Shiga-like toxin 1 and its peptide fragments indicate that the B subunit is a vaccine candidate to counter action of the toxin

The B subunit of Shiga toxin and Shiga-like toxin (SLT-1) and its fragments are potentially immunogenic and may generate protective humoral responses against the action of these toxins. We have analyzed the antibody response of rabbits immunized with pure B subunit of SLT-1 or synthetic fragments of the subunit. The immune response to the native B subunit was found to be largely directed at conformational epitopes. More importantly, rabbits immunized with the B subunit were protected from a lethal challenge with SLT-1, indicating that the B subunit represents an excellent vaccine candidate to counter the effects of Shiga toxin and SLT-1 in humans. Polyclonal antibodies against a synthetic peptide corresponding to residues 28 to 40 of the B subunit neutralized the cytotoxicity of SLT-1 towards Vero cells. This region is thus exposed in the native state of the B subunit. The sequence specificity of other antipeptide antisera also provides clues to the state of folding and assembly of the B subunit. Antisera to synthetic peptides representing the N- and C-terminal regions of the SLT-1 B subunit did not cross-react with native B subunit but strongly recognized denatured forms of the protein. Finally, the monoclonal antibody 13C4 was shown to bind to a discontinuous epitope expressed only on the native form of the protein. These immunological reagents can be used to probe the conformational state of the B subunit and the holotoxin as it relates to their functional properties.

Assessment of ischemia-induced reperfusion injury in the pig latissimus dorsi myocutaneous flap model

Experiments were conducted to assess ischemia-induced reperfusion injury in the pig latissimus dorsi myocutaneous flap model. Forty Yorkshire pigs (19.5 +/- 0.6 kg) were assigned to groups A, B, C, and D (n = 10 pigs). Bilateral 8 x 13 cm latissimus dorsi myocutaneous flaps were constructed in each pig, and one flap was assigned to ischemic treatment and the contralateral flap served as a nonischemic control. The treatment flaps in groups A, B, C, and D were subjected to 2, 4, 6, and 8 hours of warm global ischemia, respectively. Pigs in groups A, B, C, and D were divided into two subgroups (n = 5 pigs), and extents of skin and muscle necrosis in control and treatment flaps were assessed with the fluorescein and nitroblue tetrazolium dye stain tests, respectively, after 2 and 7 days of reperfusion. Significantly (p < 0.01) greater extents of skin and muscle necrosis were observed in latissimus dorsi myocutaneous flaps subjected to 4, 6, or 8 hours of ischemia compared with their contralateral controls. Extents of skin and muscle necrosis also increased significantly (p < 0.01) with increases in ischemia time in treatment flaps. Of particular importance was the observation that there was no significant difference in the extent of skin or muscle necrosis between 2 and 7 days of reperfusion in all control and treatment groups. This observation indicates that 2 days of reperfusion time is adequate to assess the maximum extent of skin and muscle ischemia-induced reperfusion injury in pig latissimus dorsi myocutaneous flaps. Furthermore, it was observed that 1-cm segments of latissimus dorsi muscle were not too thick to allow the use of the nitroblue tetrazolium dye stain test for assessment of muscle viability, as judged by the highly correlated (r = 0.98, n = 40) linear relationship between assessment of muscle viability from one transverse cut surface of muscle segments and by weighing total viable and nonviable muscles dissected from the flaps according to the nitroblue tetrazolium dye stain on both transverse cut surfaces. It is important to note that the maximum length of the latissimus dorsi myocutaneous flap model for ischemia-induced reperfusion injury research should not exceed the maximum length of skin viability in the nonischemic control in order to avoid the complication of skin necrosis due to excessive length of skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of xanthine oxidase in reperfusion injury of ischemic skeletal muscles in the pig and human

We investigated whether xanthine oxidase (XO) is a major source of oxygen-derived free radicals (oxy-radicals) in the pig and human skeletal muscles. It was observed that xanthine dehydrogenase and XO activities in nonischemic pig latissimus dorsi (LD) and gracilis muscles and human LD and rectus abdominis (RA) muscles were < 0.5 mU/g wet wt. The pig LD muscle hypoxanthine content increased significantly from 0.33 +/- 0.02 to 2.33 +/- 0.44 mumol/g dry wt after 5 h of warm ischemia, but the muscle uric acid content remained unchanged up to 2 h of reperfusion. Similarly, the hypoxanthine content in the human LD and RA muscles increased from 0.33 +/- 0.03 to 0.84 +/- 0.23 mumol/g dry wt after 2.0-3.5 h of warm ischemia, and the muscle uric acid content remained unchanged at the end of 15-90 min of reperfusion. Furthermore, 5 days of allopurinol treatment (25 mg/kg iv twice daily) starting 2 days before ischemia or 3 days of oxypurinol treatment (25 mg/kg iv twice daily) starting 15 min before reperfusion did not attenuate the extent of skeletal muscle necrosis in pig LD muscles subjected to 5 h of ischemia and 48 h of reperfusion. However, deferoxamine treatment (250 mg/kg iv twice daily) starting before or after ischemia, as described above, significantly reduced the extent of pig LD muscle necrosis. Finally, at 2 and 48 h of reperfusion significantly higher muscle neutrophil contents were seen in ischemic than in nonischemic control pig LD muscles. Neutrophil depletion with mechlorethamine (0.75 mg/kg iv) significantly reduced the extent of necrosis in pig LD muscles. These observations indicate that XO is not a major source of oxy-radicals in ischemia/reperfusion injury in the pig gracilis and LD muscles and human RA and LD muscles.

Deferoxamine attenuates ischemia-induced reperfusion injury in the skin and muscle of myocutaneous flaps in the pig

The dose effect of deferoxamine treatment in attenuation of ischemia-induced reperfusion injury in the skin and muscle of latissimus dorsi myocutaneous flaps was studied in pigs weighing 19.7 +/- 0.5 kg. The latissimus dorsi myocutaneous flaps were subjected to 4, 6, or 8 hours of warm global ischemia. The length and area of viable and nonviable skin and muscle were assessed 48 hours after the ischemic insult by using the fluorescein and nitroblue tetrazolium dye tests, respectively. It was observed that perioperative deferoxamine treatment (250 mg/kg IV) was effective (p < 0.05) in attenuation of ischemia-induced reperfusion injury in the skin but not in the muscle of latissimus dorsi myocutaneous flaps subjected to 4, 6, or 8 hours (n = 10) of ischemia compared with the saline-treated control (n = 10). In a separate study, it was observed that preoperative deferoxamine treatment (250 mg/kg per day x 2 days, IM) plus perioperative deferoxamine treatment (250 mg/kg IV) was effective (p < 0.05) in attenuation of muscle ischemia-induced reperfusion injury in latissimus dorsi myocutaneous flaps subjected to 4 hours of ischemia and 48 hours of reperfusion (n = 10) compared with the saline treated control (n = 10). Morphologic studies with light and electron microscopy also provided evidence to indicate that preoperative plus perioperative deferoxamine treatment, but not perioperative deferoxamine treatment alone, remarkably reduced ischemia-induced reperfusion injury in the skeletal muscle of latissimus dorsi myocutaneous flaps compared with the saline-treated control. It is concluded that deferoxamine is effective in the attenuation of ischemia-induced reperfusion injury in the skin and muscle of pig latissimus dorsi myocutaneous flaps, but a longer period and/or higher dose of deferoxamine treatment is required for the muscle than for the skin. The pharmacologic actions and metabolism of deferoxamine relating to mitigation of ischemia-induced reperfusion injury in the pig skin and muscle are discussed.

Primary leiomyosarcoma of the mandible in a 7-year-old girl: report of a case and review of the literature

Leiomyosarcoma is a malignant neoplasm of smooth muscle origin that manifests itself uncommonly in the oral cavity because of the paucity of smooth muscle in that location. To the best of our knowledge, only 10 cases of leiomyosarcoma primary to the jawbones have been reported in the English language literature. We report the first pediatric case of leiomyosarcoma arising from the mandible. Facial asymmetry and swelling were accompanied by a rapidly growing exophytic soft tissue mass that caused buccal displacement of the mandibular left permanent first molar. The lesion, observed radiographically as an extensive ill-defined area of osteolytic alveolar destruction, perforated the lingual cortex, displaced the inferior alveolar nerve canal inferiorly, and produced a "floating-in-air" appearance of the first molar. Diagnosis of leiomyosarcoma was made after initial incisional biopsy of the lesion. A 5-cm segmental mandibulectomy and supraomohyoid neck dissection were followed by reconstruction with a dynamic mandibular reconstruction plate and placement of a multidimensional mandibular distraction device in a transport rectangle of bone to promote bifocal distraction osteogenesis. Forty millimeters of distraction (the technical limit of the device) were performed; this was followed by terminal iliac crest bone grafting. Seventeen months after the definitive surgical procedure, the patient remains free of disease.

Application of microvascular free osteocutaneous flaps in the management of post-radiation recurrent oral cancer

Fifty-nine patients underwent free flap osteocutaneous reconstruction that consisted of flaps of the dorsum of the foot in 26 patients and iliac crest flaps in 33 with a success rate of 92 percent and a mortality rate of 1.6 percent. These flaps, which require the expertise of microvascular surgeons, are time-consuming and complicate operating room and time management, but they represent a remarkable advance in reconstruction that can facilitate cosmetic and functional recovery of the patient. In particular, they promote healing in radiation-recurrent oral cancer and represent a definitive form of management for established radionecrosis of the mandible. The large volume of tissue available with iliac crest osteocutaneous grafts permits the management of patients with extensive cancer involving the skin, mucosa, and bone, but cancer control may still be disappointing and there is a need for improved adjuvant chemotherapy protocols. This technique appears to be a dependable, repeatable, and significant advance in management of the patient with head and neck cancer.