Peripheral denervation participates in heterotopic ossification in a spinal cord injury model

We previously reported the development of a new acquired neurogenic HO (NHO) mouse model, combining spinal cord transection (SCI) and chemical muscle injury. Pathological mechanisms responsible for ectopic osteogenesis after central neurological damage are still to be elucidated. In this study, we first hypothesized that peripheral nervous system (PNS) might convey pathological signals from injured spinal cord to muscles in NHO mouse model. Secondly, we sought to determine whether SCI could lead to intramuscular modifications of BMP2 signaling pathways. Twenty one C57Bl6 mice were included in this protocol. Bilateral cardiotoxin (CTX) injection in hamstring muscles was associated with a two-stage surgical procedure, combining thoracic SCI with unilateral peripheral denervation. Volumes of HO (Bone Volume, BV) were measured 28 days after surgery using micro-computed tomography imaging techniques and histological analyses were made to confirm intramuscular osteogenesis. Volume comparisons were conducted between right and left hind limb of each animal, using a Wilcoxon signed rank test. Quantitative polymerase chain reaction (qPCR) was performed to explore intra muscular expression of BMP2, Alk3 and Id1. Nineteen mice survive the complete SCI and peripheral denervation procedure. When CTX injections were done right after surgery (n = 7), bilateral HO were detected in all animals after 28 days. Micro-CT measurements showed significantly increased BV in denervated paws (1.47 mm3 +/- 0.5) compared to contralateral sides (0.56 mm3 +/-0.4), p = 0.03. When peripheral denervation and CTX injections were performed after sham SCI surgery (n = 6), bilateral HO were present in three mice at day 28. Quantitative PCR analyses showed no changes in intra muscular BMP2 expression after SCI as compared to control mice (shamSCI). Peripheral denervation can be reliably added to spinal cord transection in NHO mouse model. This new experimental design confirms that neuro inflammatory mechanisms induced by central or peripheral nervous system injury plays a key role in triggering ectopic osteogenesis.

Marginal zinc deficiency negatively affects recovery from muscle injury in mice

The aim of the present study was to elucidate whether the recovery from muscle injury is impaired in marginal zinc deficiency. C57BL/6 male mice were fed a marginally zinc-deficient diet (MZD: 8 mg Zn/kg diet), a zinc-adequate diet (ZA: zinc 35 mg Zn/kg diet), and a zinc-high diet (ZH: 190 mg Zn/kg diet) for 4 weeks. Muscle injury was induced in the gastrocnemius muscles using cardiotoxin. The gastrocnemius muscles of these mice were harvested at 3, 5, 7, 10, 14, and 20 days after injury. We evaluated the regeneration of the skeletal muscle with hematoxylin and eosin staining and developmental myosin heavy-chain (dMHC: implicated in regeneration) immunostaining. The rate of dMHC-positive cells was significantly low in MZD mice compared with ZA mice at 3 days after cardiotoxin injection. The peak dMHC expression was found at 3 days after injection in ZA mice, 5 days in ZH mice, and 7 days in MZD mice. These results suggest that recovery from muscle injury might be partly impaired and delayed in MZD mice. Therefore, we strongly suggest the appropriate zinc intake to prevent the impairment of skeletal muscle regeneration.

Type 2 innate signals stimulate fibro/adipogenic progenitors to facilitate muscle regeneration

In vertebrates, activation of innate immunity is an early response to injury, implicating it in the regenerative process. However, the mechanisms by which innate signals might regulate stem cell functionality are unknown. Here, we demonstrate that type 2 innate immunity is required for regeneration of skeletal muscle after injury. Muscle damage results in rapid recruitment of eosinophils, which secrete IL-4 to activate the regenerative actions of muscle resident fibro/adipocyte progenitors (FAPs). In FAPs, IL-4/IL-13 signaling serves as a key switch to control their fate and functions. Activation of IL-4/IL-13 signaling promotes proliferation of FAPs to support myogenesis while inhibiting their differentiation into adipocytes. Surprisingly, type 2 cytokine signaling is also required in FAPs, but not in myeloid cells, for rapid clearance of necrotic debris, a process that is necessary for timely and complete regeneration of tissues.

Xin, an actin binding protein, is expressed within muscle satellite cells and newly regenerated skeletal muscle fibers

Xin is a muscle-specific actin binding protein of which its role and regulation within skeletal muscle is not well understood. Here we demonstrate that Xin mRNA is robustly upregulated (>16-fold) within 12 h of skeletal muscle injury and is localized to the muscle satellite cell population. RT-PCR confirmed the expression pattern of Xin during regeneration, as well as within primary muscle myoblast cultures, but not other known stem cell populations. Immunohistochemical staining of single myofibers demonstrate Xin expression colocalized with the satellite cell marker Syndecan-4 further supporting the mRNA expression of Xin in satellite cells. In situ hybridization of regenerating muscle 5-7 days postinjury illustrates Xin expression within newly regenerated myofibers. Promoter-reporter assays demonstrate that known myogenic transcription factors [myocyte enhancer factor-2 (MEF2), myogenic differentiation-1 (MyoD), and myogenic factor-5 (Myf-5)] transactivate Xin promoter constructs supporting the muscle-specific expression of Xin. To determine the role of Xin within muscle precursor cells, proliferation, migration, and differentiation analysis using Xin, short hairpin RNA (shRNA) were undertaken in C2C12 myoblasts. Reducing endogenous Xin expression resulted in a 26% increase (P < 0.05) in cell proliferation and a 20% increase (P < 0.05) in myoblast migratory capacity. Skeletal muscle myosin heavy chain protein levels were increased (P < 0.05) with Xin shRNA administration; however, this was not accompanied by changes in myoglobin protein (another marker of differentiation) nor overt morphological differences relative to differentiating control cells. Taken together, the present findings support the hypothesis that Xin is expressed within muscle satellite cells during skeletal muscle regeneration and is involved in the regulation of myoblast function.

Effects of functional overloading on the regenerative potential of injured skeletal muscles in mice

The purpose of this study was to investigate the effects of functional overload on the regeneration of injured skeletal muscles of male C57BL/6J mice. To activate a necrosis-regeneration cycle, cardiotoxin (CTX) was injected into soleus muscles both control and functionally overloaded groups. The recovery of muscle protein content, which was decreased by CTX injection, was significantly stimulated by application of functional overloading. The CTX-injection-related increment of satellite cell number in the overloaded groups was also greater than that in the group without overloading. Evidences suggest that the application of a mechanical stress on the injured skeletal muscles could activate satellite cells and facilitate the regeneration of the muscle.

The urokinase-type plasminogen activator receptor is not required for skeletal muscle inflammation or regeneration

The hypothesis of this study was the urokinase-type plasminogen activator receptor (uPAR) is required for accumulation of inflammatory cells in injured skeletal muscle and for efficient muscle regeneration. Expression of uPAR was elevated at 1 and 3 days after cardiotoxin-induced muscle injury in wild-type mice before returning to baseline levels. Neutrophil accumulation peaked 1 day postinjury in muscle from both wild-type (WT) and uPAR null mice, while macrophage accumulation peaked between 3 and 5 days postinjury, with no differences between strains. Histological analyses confirmed efficient muscle regeneration in both wild-type and uPAR null mice, with no difference between strains in the formation or growth of regenerating fibers, or recovery of normal morphology. Furthermore, in vitro experiments demonstrated that chemotaxis is not different between WT and uPAR null macrophages. Finally, fusion of cultured satellite cells into multinucleated myotubes was not different between cells isolated from WT and uPAR null mice. These results demonstrate that uPAR is not required for the accumulation of inflammatory cells or the regeneration of skeletal muscle following injury, suggesting uPA can act independently of uPAR to regulate events critical for muscle regeneration.

Delayed angiogenesis and VEGF production in CCR2-/- mice during impaired skeletal muscle regeneration

The regulation of vascular endothelial growth factor (VEGF) levels and angiogenic events during skeletal muscle regeneration remains largely unknown. This study examined angiogenesis, VEGF levels, and muscle regeneration after cardiotoxin (CT)-induced injury in mice lacking the CC chemokine receptor 2 (CCR2). Muscle regeneration was significantly decreased in CCR2-/- mice as was the early accumulation of macrophages after injury. In both mouse strains, tissue VEGF was similar at baseline (no injections) and significantly decreased at day 3 post-CT. Tissue VEGF in wild-type (WT) mice was restored within 7 days postinjury but remained significantly reduced in CCR2-/- mice until day 21. Capillary density (capillaries/mm(2)) within regenerating muscle was maximal in WT mice at day 7 and double that of baseline muscle. In comparison, maximal capillary density in CCR2-/- mice occurred at 21 days postinjury. Maximal capillary density developed concurrent with the restoration of tissue VEGF in both strains. A highly significant, inverse relationship existed between the size of regenerated muscle fibers and capillaries per square millimeter. Although this relationship was comparable in WT and CCR2-/- animals, there was a significant decrease in the magnitude of this response in the absence of CCR2, reflecting the observation that regenerated muscle fiber size in CCR2-/- mice was only 50% of baseline at 42 days postinjury, whereas WT mice had attained baseline fiber size by day 21. Thus CCR2-dependent events in injured skeletal muscle, including impaired macrophage recruitment, contribute to restoration of tissue VEGF levels and the dynamic processes of capillary formation and muscle regeneration.

Differential recovery of neuromuscular function after nerve/muscle injury induced by crude venom from Notechis scutatus, cardiotoxin from Naja atra and bupivacaine treatments in mice

Different neuromyotoxic agents are frequently used in rodent models of skeletal nerve/muscle injury and repair. However, their differential effects are not well known. Right Tibialis anterior muscles of mice were injured by one of three different neuromyotoxic agents: crude venom from Notechis scutatus, cardiotoxin from Naja atra or bupivacaine (local anesthetic). Mice were studied 5, 14 and 56 days after injury by analysing the recovery of in situ muscle isometric function in response to nerve stimulation, muscle weights and muscle histology. Our results show that at day 5 venom treatment had a more debilitating effect on muscle weights and maximal tetanic force than cardiotoxin and bupivacaine treatments (p<0.05). Moreover, the degree of recovery of muscle parameters 14 days after neuromyotoxic treatment varies as follow: venom<bupivacaine<cardiotoxin. By day 56, we found that injured muscles still exhibit deficits in maximal tetanic force (cardiotoxin and bupivacaine treatments) and fatigue resistance (venom and cardiotoxin treatments) as compared to control muscles (p<0.05). In conclusion, these results indicate that neuromyotoxic agents induce differential destructive effects and recovery in mice and confirm the fact that full nerve/muscle repair is slow and in some cases may never be attained.

TNF-alpha regulates myogenesis and muscle regeneration by activating p38 MAPK

Although p38 MAPK activation is essential for myogenesis, the upstream signaling mechanism that activates p38 during myogenesis remains undefined. We recently reported that p38 activation, myogenesis, and regeneration in cardiotoxin-injured soleus muscle are impaired in TNF-alpha receptor double-knockout (p55(-/-)p75(-/-)) mice. To fully evaluate the role of TNF-alpha in myogenic activation of p38, we tried to determine whether p38 activation in differentiating myoblasts requires autocrine TNF-alpha, and whether forced activation of p38 rescues impaired myogenesis and regeneration in the p55(-/-)p75(-/-) soleus. We observed an increase of TNF-alpha release from C2C12 or mouse primary myoblasts placed in low-serum differentiation medium. A TNF-alpha-neutralizing antibody added to differentiation medium blocked p38 activation and suppressed differentiation markers myocyte enhancer factor (MEF)-2C, myogenin, p21, and myosin heavy chain in C2C12 myoblasts. Conversely, recombinant TNF-alpha added to differentiation medium stimulated myogenesis at 0.05 ng/ml while inhibited it at 0.5 and 5 ng/ml. In addition, differentiation medium-induced p38 activation and myogenesis were compromised in primary myoblasts prepared from p55(-/-)p75(-/-) mice. Increased TNF-alpha release was also seen in cardiotoxin-injured soleus over the course of regeneration. Forced activation of p38 via the constitutive activator of p38, MKK6bE, rescued impaired myogenesis and regeneration in the cardiotoxin-injured p55(-/-)p75(-/-) soleus. These results indicate that TNF-alpha regulates myogenesis and muscle regeneration as a key activator of p38.

Effects of eccentric treadmill running on mouse soleus: degeneration/regeneration studied with Myf-5 and MyoD probes

AIM

The aim of this report is to show that eccentric exercise under well-controlled conditions is an alternative model, to chemical and mechanical analyses, and analyse the process of degeneration/regeneration in mouse soleus.

METHODS

For this, mice were submitted to a single bout of eccentric exercise on a treadmill down a 14 degrees decline for 150 min and the soleus muscle was analysed at different times following exercise by histology and in situ hybridization in comparison with cardiotoxin-injured muscles.

RESULTS

We analyse the regenerative process by detection of the accumulation of transcripts coding for the two myogenic regulatory factors, Myf-5 and MyoD, which are good markers of the activated satellite cells. From 24 h post-exercise (P-E), clusters of mononucleated Myf-5/MyoD-positive cells were detected. Their number increased up to 96 h P-E when young MyoD-positive myotubes with central nuclei began to appear. From 96 to 168 h P-E the number of myotubes increased, about 10-fold, the new myotubes representing 58% of the muscle cells (168 h P-E).

CONCLUSION

These results show that this protocol of eccentric exercise is able to induce a drastic degeneration/regeneration process in the soleus muscle. This offers the opportunity to perform biochemical and molecular analyses of a process of regeneration without muscle environment defects. The advantages of this model are discussed in the context of fundamental and therapeutical perspectives.

Expression and neural control of myogenic regulatory factor genes during regeneration of mouse soleus

Given the importance of the myogenic regulatory factors (MRFs) for myoblast differentiation during development, the aims of this work were to clarify the spatial and temporal expression pattern of the four MRF mRNAs during soleus regeneration in mouse after cardiotoxin injury, using in situ hybridization, and to investigate the influence of innervation on the expression of each MRF during a complete degeneration/regeneration process. For this, we performed cardiotoxin injury-induced regeneration experiments on denervated soleus muscle. Myf-5, MyoD, and MRF4 mRNAs were detected in satellite cell-derived myoblasts in the first stages of muscle regeneration analyzed (2--3 days P-I). The Myf-5 transcript level dramatically decreased in young multinucleated myotubes, whereas MyoD and MRF4 transcripts were expressed persistently throughout the regeneration process. Myogenin mRNA was transiently expressed in forming myotubes. These results are discussed with regard to the potential relationships between MyoD and MRF4 in the satellite cell differentiation pathway. Muscle denervation precociously (at 8 days P-I) upregulated both the Myf-5 and the MRF4 mRNA levels, whereas the increase of both MyoD and myogenin mRNA levels was observed later, in the late stages of regeneration (30 days P-I). This significant accumulation of each differentially upregulated MRF during soleus regeneration after denervation suggests that each myogenic factor might have a distinct role in the regulatory control of muscle gene expression. This role is discussed in relation to the expression of the nerve-regulated genes, such as the nAChR subunit gene family. (J Histochem Cytochem 49:887-899, 2001)

Differential modulation of alpha, beta and gamma enolase isoforms in regenerating mouse skeletal muscle

Nothing is known about the expression of the glycolytic enzyme enolase in skeletal muscle alterations such as myofiber degeneration and regeneration. Enolase is a dimeric enzyme which exhibits cell type specific isoforms. The embryonic form, alphaalpha, remains expressed in most adult tissues, whereas a transition towards specific isoforms occurs during ontogenesis in two cell types with high energy requirements: alphagamma and gammagamma in neurons, alphabeta and betabeta in striated muscle cells. During murine myogenesis, beta enolase transcripts are detected early in the forming muscles, and the beta gene is further upregulated at specific stages of muscle development. The alpha and beta subunits exhibit characteristic developmental microheterogeneity patterns. High levels of beta enolase subunits characterize the glycolytic fast-twitch fibers of adult muscles. We have investigated the expression of enolase subunits in a mouse experimental model of muscle regeneration. Following a single intramuscular injection of the necrotic agent cardiotoxin, we observed a rapid decrease in the level of the major muscle enolase subunit beta, accounting for the drop in total enolase activity that correlated with the degeneration of myofibers. Concomitant with the regeneration of new fibers, beta subunit levels began to increase, reaching normal values by 30 days after injury. Changes in the embryonic and ubiquitous subunit, alpha, mimicked those occurring during development by two aspects: modifications in electrophoretic variants and redistribution between soluble and insoluble compartments of muscle extracts. Imunocytochemical analyses of alpha and beta enolase subunits first revealed a homogeneous labeling within myofibers. Striations characteristic of normal adult muscle tissue were visible again by day 14 after injury. A perinuclear alpha and beta immunoreactivity was often observed in regenerating myofibers but its functional significance remains to be elucidated. Double labeling experiments with anti-gamma enolase and FITC-alpha bungarotoxin allowed us to follow the neuromuscular junction remodeling that occurs during muscle regeneration despite the absence of nerve injury.

Expression of matrix metalloproteinases 2 and 9 in regenerating skeletal muscle: a study in experimentally injured and mdx muscles

Matrix metalloproteinases (MMPs) cooperatively degrade all components of the extracellular matrix (ECM). Remodeling of ECM during skeletal muscle degeneration and regeneration suggests a tight regulation of matrix-degrading activity during muscle regeneration. In this study, we investigated the expression of MMP-2 and MMP-9, in normal muscles and their regulation during regeneration process. We further investigated their secretion by C2C12 myogenic cell line. Two models of muscle degeneration-regeneration were used: (1) normal muscles in which necrosis was experimentally induced by cardiotoxin injection; (2) mdx muscles which exhibit recurrent signs of focal myofiber necrosis followed by successful regeneration. MMPs were studied by zymography; their free activity was quantified using 3H-labeled gelatin substrate and mRNA expression was followed by Northern hybridization. Muscle degeneration-regeneration was analyzed by conventional morphological methods and in situ hybridization was performed on muscle sections to identify the cells expressing these MMPs. Results show that MMP-2, but not MMP-9 expression, is constitutive in normal muscles. Upon injury, the active form of MMP-2 is transiently increased, whereas MMP-9 is induced within 24 h and remains present for several days. Quantitative assays of free gelatinolytic activity show a progressive and steady increase that culminates at 7 days postinjury and slowly returns to normal levels. In adult mdx mice, both pro and active forms of MMP-2 and MMP-9 are expressed. Northern blot results support these findings. Zymography of C2C12-conditioned medium shows that myogenic cells produce MMP-2. By in situ hybridization we localized MMP-9 mRNA in inflammatory cells and putative activated satellite cells in injured muscles. Our data allow the correlation of the differential expression of pro and/or active forms of MMP-2 and MMP-9 with different stages of the degeneration-regeneration process: MMP-9 expression is related to the inflammatory response and probably to the activation of satellite cells, whereas MMP-2 activation is concomitant with the regeneration of new myofibers.

Bubble recycling and ultrasonic cell lysis in a stationary exposure vessel

An exposure system producing interleafed pulses of 1-MHz ultrasound from balanced, opposing transducers was used to test the bubble recycling hypothesis (as formulated with respect to rotating exposure vessels) in a stationary exposure vessel containing P388 cell suspensions. Cell lysis was measured in cell suspensions which had been exposed or sham-exposed to 1-MHz ultrasound (5 W/cm2 spatial peak pulse average intensity) delivered in continuously alternating, opposing pulses. The opposing pulse cycle frequency (i.e., gating frequency) varied from 0.1 Hz to 100 kHz, corresponding to single pulse durations ranging from 5 microseconds to 5 s. Unequivocal support for the bubble recycling hypothesis was obtained. Lytic yield increased as the gating frequency increased, passing through a maximum at gating frequencies of 100 Hz-1 kHz. As the gating frequency increased further, lytic yield declined rapidly. The results are discussed in relation to recent theoretical estimates of bubble translation speeds in an ultrasound field, and are found to be consistent with those estimates.

Cardiotoxin VII4 from Naja mossambica mossambica. The refined crystal structure

The crystal structure of cardiotoxin VII4 from Naja mossambica mossambica was refined to 2.5 A resolution. Fifty ordered solvent sites were localized and included in the refinement. The final R factor is 0.197 (lambda/(2sin theta) less than 5 A; F greater than 3 sigma). The three-dimensional structure is characterized by two beta-sheets. Of particular interest is the two-stranded beta-sheet in the N-terminal region. This shows a large right-handed twist and, though strongly connected to the core of the molecule, and in particular to the C-terminal end, protrudes out of the bulk of the molecule. The segment of four amino acid residues connecting the two strands of this sheet is particularly exposed. It contains an invariant proline residue that has probably an important structural role, and is completely hydrophobic. Two other conserved hydrophobic zones were identified; the largest extends over the second and third loops, on one side only of the molecule. All side-chains of invariant hydrophobic character (except proline residues) belong to one of these three zones. Also discussed are the dimeric assembly and the rather loose packing in the crystal. The three-dimensional structure is compared with that of short and long alpha-neurotoxins. Comparison with two-dimensional nuclear magnetic resonance results on the 68% homologous cardiotoxin CT X IIb shows an excellent overall agreement. A few differences are probably genuine.

Circular dichroic spectra of elapid cardiotoxins

Cardiotoxins isolated from elapid snake venoms constitute a chemically homogeneous family of molecules. Within this group several biologically different subclasses exist. We report a comparative analysis of the structure of 20 cardiotoxins using circular dichroism, immunological methods and secondary-structure prediction. It is shown that cardiotoxins fall within two structural subclasses. Toxins of group I are characterized by (a) CD spectra having an intense positive band close to 192.5 nm and a negative trough at 225 nm with no positive band around 230 nm, (b) strong cross-reactivity with a polyclonal antiserum specific for Naja nigricollis toxin gamma and (c) a high tendency to form a reverse turn in the region of position 11. Toxins of group II are characterized by (a) CD spectra displaying a much weaker positive band at 192.5 nm, a negative band around 210 nm and a positive band at 230 nm, (b) little cross-reactivity with the aforementioned antiserum and (c) a high reverse-turn potential at position 31. It is suggested that the observed differences result from differing curvatures in the antiparallel beta sheet which constitutes the main secondary structure of cardiotoxins.

Mixed phospholipid-cardiotoxin monomolecular films studied by intrinsic polarized surface fluorescence

Surface fluorescence spectroscopy was used to study mixed phospholipid-cardiotoxin monomolecular films. Using polarized incident light we were able to detect the intrinsic fluorescence emission at a wavelength of 339 nm of the single Trp11 in the cardiotoxin molecule. Its fluorescence intensity increased continuously upon film compression up to a maximal value reached at 42 mN x m-1 in surface pressure. A relative polarization index can be used as an indication of the orientation of the indole ring. A transition at around 25 +/- 5 mN x m-1 in the orientation of the Trp11 relative to the plane of the interface was clearly evidenced during film compression, in agreement with our independent data showing a flipping of the whole toxin molecule (Bougis et al., (1981), Biochemistry 20, 4915-4920).

Penetration of a cardiotoxin into cardiolipin model membranes and its implications on lipid organization

The interaction of cardiotoxin II of Naja mossambica mossambica with cardiolipin model membranes was investigated by binding, fluorescence, resonance energy transfer, fluorescence quenching, 31P NMR, freeze-fracture, and small-angle X-ray experiments. An initially electrostatic binding appeared to be accompanied by a deep penetration, most likely into the acyl chain region of the phospholipids, indicating a hydrophobic contribution to the strong interaction (KD congruent to 5 X 10(-8) M). This binding results in a fusion of unilamellar vesicles as indicated by a fluorescence-based fusion assay, freeze-fracture, and X-ray diffraction. In these fused structures freeze-fracture electron microscopy reveals the appearance of particles, which is accompanied by the induction of an isotropic component in 31P NMR. The well-defined particles are interpreted as inverted micelles, and the localization of the cardiotoxin molecule in these structures is discussed.

Abolition of the thermotropic transition of charged phospholipids induced by a cardiotoxin from Naja mossambica mossambica as detected by fluorescence polarization, differential scanning calorimetry, and Raman spectroscopy

The effects of a Naja mossambica mossambica cardiotoxin on the thermotropic properties of charged phospholipids have been studied by fluorescence polarization, differential scanning calorimetry, and Raman spectroscopy. The binding of the toxin is only governed by the net charge at the interface and is not affected by the polar head group structure of the phospholipids or by the acyl chains physical state, degree of insaturation, or length. The effect of the toxin on the phospholipid structure is drastic. In all cases, the gel to liquid-crystalline phase transition monitored by fluorescence and Raman spectroscopies is progressively abolished without notable shift in temperature as the proportion of toxin is increased. The endothermic peaks detected by differential scanning calorimetry decrease in intensity as the toxin content is increased but always remain sharp. All the techniques used give complementary results, and none of them reveals the presence of secondary transitions at higher or lower temperatures. We thus believe that the lipid molecules that are perturbed by the toxin, approximately 10 +/- 2 molecules, do not undergo a phase transition. Raman results demonstrate that these "boundary" lipids display a population of gauche rotamers that is as high as the one found in the liquid-crystalline phase of the pure phospholipid and this even well below the phase transition temperature. On the other hand, fluorescence results are interpreted as due to a partial immobilization of the lipids in contact with the toxin above the transition temperature. Thus, even though the interaction is governed by electrostatic forces, the toxin penetrates at least partially into the bilayers, inducing a disorganization of the aliphatic chains and changes in their mobility; this could explain their lytic activity.

Sequential individual resonance assignments in the 1H nuclear-magnetic-resonance spectrum of cardiotoxin VII2 from Naja mossambica mossambica

The assignment of the 1H nuclear magnetic resonance (NMR) spectrum of cardiotoxin VII2 from Naja mossambica mossambica is described and documented. The assignments are based entirely on the amino acid sequence and on two-dimensional NMR experiments at 500 MHz. Individual assignments were obtained at 45 degrees C for the backbone protons of 56 out of the total of 60 amino acid residues, the exceptions being the N-terminal dipeptide segment Leu-1--Lys-2--, Pro-8 and Pro-15. Complete assignments of the non-labile hydrogen atoms of the side chains were obtained for 37 residues, and for Asn-4 and Asn-19 the delta amide protons were also identified. For 19 long side chains the individual assignments include only the backbone and C-beta proton resonances; these are Gln-5, Pro-9, Pro-33, Pro-43, Leu-47, all three methionines, two arginines and nine lysines. The chemical shifts for the assigned resonances at 45 degrees C are listed for an aqueous solution at pH 3.6. A preliminary interpretation of the sequential connectivity patterns indicates that approximately 30 out of the total of 60 amino acid residues in cardiotoxin VII2 are in extended, beta-type secondary structures, and there is no indication for the formation of alpha-helical structure.

A possible orientation change of cardiotoxin molecule during its interaction with phospholipid monolayer

The monomolecular film technique was used in order to study the specific interactions of 4 cardiotoxins from Elapidae snake venom Naja mossambica mosambica with different phospholipids. The interaction, at pH 7.5, of cardiotoxin (10(-7) M) with both neutral and negatively charged phospholipids occurs up to a very high critical surface pressure (pi = 45 dynes/cm with the latest). The apparent molecular area of cardiotoxin molecule, during its insertion into a negatively charged phospholipid film, presents only two characteristic values: 1400 A2 for pi less than 20 dynes/cm and 420 A2 for pi greater than 30 dynes/cm, the transition occurring in a very narrow range of surface pressure (25 +/- 5 dynes/cm). Thus, according to the surface pressure, the cardiotoxin may present two different orientations: "flat" or "edgewise" and the transition between both could account for lytic activity of cardiotoxin.

Structure-function relationships for cardiotoxins interacting with phospholipids

Four cardiotoxins (CTX I-IV) from Naja mossambica mossambica were compared for their ability to interact with phospholipid vesicles and their capacity to bind erythrocytes. It is concluded that the affinity of the toxins always increases in the order: I approximately equal to II less than III less than IV. The binding is specific for charged lipids even in lipid mixtures. Proteolytic attack of the free and lipid-bound cardiotoxin indicates that at least the first loop Leu1-Thr13 is at the lipid contact. Tryptic and synthetic peptides constitutive of this loop are shown to interact with lipids. Arg5 residue increases the affinity toward the bilayer. The Raman spectra of lipid-bound cardiotoxin indicate a secondary and tertiary structure mainly similar to that of the free toxin. On charged lipids cardiotoxins induce a decrease of the enthalpy and an increase of disorder without change in the transition temperature; at saturating amounts of toxin the transition is abolished. In binary mixtures of phosphatidylcholine and charged lipids the observed effects can be accounted by a phase separation induced by the toxin.

Penetration of phospholipid monolayers by cardiotoxins

The monomolecular film technique was used to compare the specific interaction of four cardiotoxins from Naja mossambica mossambica with different phospholipids. We were able to demonstrate the interaction of cardiotoxins (10(-7) M) with both neutral and negatively charged phospholipids up to very high surface pressures (45 dyn/cm). In the presence of a phospholipid monolayer, the surface activity of cardiotoxins became much greater than that observed at the air-water interface. Neurotoxins of the same venom do not penetrate a phospholipid film, even at low surface pressure (15 dyn/cm). The apparent molecular area of cardiotoxin III during its insertion into a negatively charged phospholipid film was quantitatively defined. As a function of surface pressure of the membrane around 25 dyn/cm, cardiotoxins may exist in two different configurations, "flat" (1400 A2) or "edgewise" (420 A2). This result could account for the lytic activity of this type of toxin.

The preparation of 3-nitrotyrosyl derivatives of three elapid venom cardiotoxins

Nitration studies using tetranitromethane were conducted on the tyrosine residues of cardiotoxins, naja melanoleuca VII1, Naja haje annulifera VII1 and Hemachatus haemachates toxin 12B. Various partially and fully nitrated derivatives were formed. Analysis of the products of nitrating naja melanoleuca VII1 showed that the average relative reactivities of the three tyrosine residues were Tyr-25 greater than Tyr-22 greater than Tyr-51. It was significant that Tyr-51 could be easily modified in both N. melanoleuca VII1 and N. haje annulifera VII1. In contrast, other workers had found Tyr-51 in N. naja atra cardiotoxin to be unreactive towards tetranitromethane except under denaturing conditions. Fully nitrated derivatives of N. melanoleuca VII1 (Tyr-22, -25 and -51), N haje annulifera VII1 (Tyr-22 and -51) and H. haemachates 12B (Tyr-22), prepared under mild reaction conditions, were isolated by ion-exchange and hydrophobic interaction chromatographies. All three derivatives were pure by disc gel electrophoresis at pH 8.9 and amino acid analysis. They were therefore suitable for spectral and biological studies. The results were compared and contrasted to; those of other workers.

The 1H nuclear-magnetic-resonance spectra of Neurotoxin I and cardiotoxin Vii4 from Naja mossambica mossambica

Two toxins from the venom of Naja mossambica mossambica, neurotoxin I and cardiotoxin VII4, were investigated in aqueous solution by high-resolution 1H nuclear magnetic resonance (NMR) techniques at 360 MHz. The spectral characterization of the proteins included determination of the number of slowly exchanging amide protons which can be observed in 2H2O solution, measurement of the amide proton chemical shifts and exchange rates, characterization of the aromatic spin systems and the internal mobilities of aromatic rings, and studies of the pH dependence of the NMR spectra. For numerous resonances of labile and non-labile protons quite outstanding pH titration shifts were observed. It is suggested that these NMR parameters provide a useful basis for comparative structural studies of different proteins in the large group of homologous snake toxins. As a first application the NMR data presently available in the literature on neurotoxin II from Naja naja oxiana, toxin alpha from Naja nigricollis and erabutoxin a and b from Laticauda semifasciata have been used to compare these three proteins with neurotoxin I from Naja mossambica mossambica. This preliminary comparative study provides evidence that the same type of spatial structure prevails for these four homologous neurotoxins and that the folding of the backbone corresponds quite closely to that observed in the crystal structure of erabutoxin b. A second application is the comparison of cardiotoxin VII4 from Naja mossambica mossambica with the neurotoxins. The experimental data indicate that the folding of the polypeptide backbone is closely similar, but that the cardiotoxin molecule is markedly more flexible than the neurotoxins.

Conformation of snake toxic polypeptides studied by a method of prediction and circular dichroism

Short and long neurotoxins as well as cardiotoxins belong to three distinct families of homologous toxic polypeptides extracted from cobra venoms. A study of their conformation was undertaken by using the method of Chou and Fasman for prediction of secondary structures of proteins. To improve the reliability of this method, an averaging scheme was developed. The data obtained showed that all toxins have a predominant trend for beta-sheet nucleation. Moreover, predicted beta-sheet strands fitted well those actually observed from X-ray data. Thus, it seems that all toxins share similarities in their secondary structure. This proposition was supported by a comparative study of the CD spectra of a set of toxins. Nevertheless, the present data suggest also that each type of toxins possesses localized structural individualities which might be responsible for the biological and/or immunological specificities.

[Heat denaturation of hemocytocardiotoxin from the venom of the Central Asian cobra]

It has been stated that boiled for three hours haemocytocardiotoxin (HT) from cobra poison loses "direct" hemolytic activity and is unable to potentiate a haemolytic effect of phospholipase A. Surface activity of HT does not change. It is shown that in the course of heat denaturation the aggregation of toxin molecules to dimers and trimers takes place and electrophoretic mobility is decreased. The fluorescence of HT tyroxin residues supported the fact of its irreversible heat denaturation.