Terence M. Myckatyn

Predictors of death in nonruptured and ruptured abdominal aortic aneurysms

PURPOSE This study evaluated perioperative variables to predict death in nonruptured and ruptured abdominal aortic aneurysm (AAA) surgery. METHODS A consecutive review of all patients who underwent AAA surgery from January 1984 to December 1993 was carried out. Perioperative variables were analyzed with univariate and multivariate statistical models to predict mortality rates. RESULTS Four hundred seventy-eight patients with nonruptured AAAs and 157 patients with ruptured AAAs were studied. In patients with nonruptured AAAs, the mortality rate was 3.8%. Using stepwise logistic regression analysis, independent predictors of death were perioperative myocardial infarction (odds ratio [OR], 5.0; p < 0.01), prolonged postoperative ventilation (OR, 4.0; p < 0.01), history of peripheral vascular disease (OR, 2.9; p < 0.01), preoperative renal dysfunction (OR, 2.7; p < 0.01), and history of congestive heart failure (OR, 2.6; p < 0.03). In patients with ruptured AAAs, the mortality rate was 46%. Analysis of preoperative variables using multivariate stepwise logistic regression found predictors of death to be preoperative unconsciousness (OR, 3.1; p < 0.01), advanced age (OR, 1.9; p < 0.01), and cardiac arrest (OR, 1.8; p < 0.05). In patients who survived the initial surgery for ruptured AAA, a second stepwise logistic regression model found independent predictors for subsequent postoperative death to be coagulation disorder (OR, 7.9; p < 0.01), ischemic colitis (OR, 6.4; p < 0.01), inotropic support beyond 48 hours (OR, 4.8; p < 0.01), delayed transport to operating room (OR, 4.6; p < 0.01), advanced age (OR, 4.4; p < 0.01), perioperative myocardial infarction (OR, 4.0; p < 0.05) and postoperative renal dysfunction (OR, 3.7; p < 0.01). CONCLUSION Prolonged ventilation, perioperative myocardial infarction, a history of peripheral vascular disease, preoperative renal dysfunction, and a history of congestive heart failure are independent predictors of perioperative death in patients with nonruptured AAAs. For patients with ruptured AAAs, mortality rates can be estimated before surgery using age, level of consciousness, and cardiac arrest. For patients who survive the initial surgery for ruptured AAA, subsequent mortality rates can also be predicted.

Binary imaging analysis for comprehensive quantitative histomorphometry of peripheral nerve.

Quantitative histomorphometry is the current gold standard for objective measurement of nerve architecture and its components. Many methods still in use rely heavily upon manual techniques that are prohibitively time consuming, predisposing to operator fatigue, sampling error, and overall limited reproducibility. More recently, investigators have attempted to combine the speed of automated morphometry with the accuracy of manual and semi-automated methods. Systematic refinements in binary imaging analysis techniques combined with an algorithmic approach allow for more exhaustive characterization of nerve parameters in the surgically relevant injury paradigms of regeneration following crush, transection, and nerve gap injuries. The binary imaging method introduced here uses multiple bitplanes to achieve reproducible, high throughput quantitative assessment of peripheral nerve. Number of myelinated axons, myelinated fiber diameter, myelin thickness, fiber distributions, myelinated fiber density, and neural debris can be quantitatively evaluated with stratification of raw data by nerve component. Results of this semi-automated method are validated by comparing values against those obtained with manual techniques. The use of this approach results in more rapid, accurate, and complete assessment of myelinated axons than manual techniques.

Muscle-derived but not centrally derived transgene GDNF is neuroprotective in G93A-SOD1 mouse model of ALS

Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for motoneurons (MNs), and is considered a potential agent for the treatment of amyotrophic lateral sclerosis (ALS) and other MN diseases. The effectiveness of GDNF may depend significantly upon its route of delivery to MNs. In this study we tested the neuroprotective effects of target-derived and centrally derived GDNF in the G93A-SOD1 mouse model of ALS using a transgenic approach. We found that overexpression of GDNF in the skeletal muscle (Myo-GDNF mice) significantly delayed the onset of disease and increased the life span of G93A-SOD1 mice by 17 days. The duration of disease also increased by 8.5 days, indicating that GDNF slowed down the progression of disease. Locomotor performance in Myo-GDNF/G93A-SOD1 mice was also significantly improved. The behavioral improvement correlated well with anatomical and histological data. We demonstrated that muscle-derived GDNF resulted in increased survival of spinal MNs, and twice as many MNs survived in end-stage double transgenic mice compared to end-stage G93A-SOD1 mice. Muscle-derived GDNF also had profound effects on muscle innervation and axonal degeneration. Significantly higher numbers of completely or partially innervated NMJs and large caliber myelinated axons were found in double transgenic mice. In contrast, we demonstrated that overexpression of GDNF in astrocytes in the CNS (GFAP-GDNF mice) failed to demonstrate any neuroprotective effects in G93A-SOD1 mice both on behavioral and histological levels. These data indicate that retrograde transport and signaling of GDNF is more physiological and effective for ALS treatment than anterogradely transported GDNF.

Choosing the correct functional assay: a comprehensive assessment of functional tests in the rat.

While there are several ways to quantify peripheral nerve regeneration; the true measure of successful outcome is functional recovery. Functional tests are relatively easily conducted in human subjects; however it is more difficult in a laboratory animal. The laboratory rat is an excellent animal model of peripheral nerve injury and has been used extensively in the field of peripheral nerve research. Due to the intense interest in the rat as an experimental model, functional assays have been reported. In an effort to provide a resource to which investigators can refer when considering the most appropriate functional assay for a given experiment, the authors have compiled and tabulated the available functional tests applicable to various models of rat nerve injury.

Reinnervation of the tibialis anterior following sciatic nerve crush injury: A confocal microscopic study in transgenic mice

Transgenic mice whose axons and Schwann cells express fluorescent chromophores enable new imaging techniques and augment concepts in developmental neurobiology. The utility of these tools in the study of traumatic nerve injury depends on employing nerve models that are amenable to microsurgical manipulation and gauging functional recovery. Motor recovery from sciatic nerve crush injury is studied here by evaluating motor endplates of the tibialis anterior muscle, which is innervated by the deep peroneal branch of the sciatic nerve. Following sciatic nerve crush, the deep surface of the tibialis anterior muscle is examined using whole mount confocal microscopy, and reinnervation is characterized by imaging fluorescent axons or Schwann cells (SCs). One week following sciatic crush injury, 100% of motor endplates are denervated with partial reinnervation at 2 weeks, hyperinnervation at 3 and 4 weeks, and restoration of a 1:1 axon to motor endplate relationship 6 weeks after injury. Walking track analysis reveals progressive recovery of sciatic nerve function by 6 weeks. SCs reveal reduced S100 expression within 2 weeks of denervation, correlating with regression to a more immature phenotype. Reinnervation of SCs restores S100 expression and a fully differentiated phenotype. Following denervation, there is altered morphology of circumscribed terminal Schwann cells demonstrating extensive process formation between adjacent motor endplates. The thin, uniformly innervated tibialis anterior muscle is well suited for studying motor reinnervation following sciatic nerve injury. Confocal microscopy may be performed coincident with other techniques of assessing nerve regeneration and functional recovery.

A review of research endeavors to optimize peripheral nerve reconstruction

Abstract This manuscript reviews studies relating to peripheral nerve allografts, neuroregenerative agents and end-to-side neurorrhaphy. With respect to peripheral nerve allografts, animal studies with the agents cyclosporin A, FK506 and rapamycin are reviewed and related to recent clinical experience. FK506 distinguishes itself as an agent capable of reversing acute rejection of a peripheral nerve allograft and an agent with some neuroregenerative properties. In addition to systemic immunosuppression, experience with agents purported to initiate a state of donor specific tolerance are discussed. Specifically, experimental studies with administration of ultraviolet B treated donor splenocytes, antibodies to cellular adhesion molecules and antibodies to components of the costimulatory pathway of immunosuppression are reviewed. The neuroregenerative properties of FK506 and related compounds are examined in animal models. Finally, the experimental finding that reinnervation following end-to-side neurorrhaphy is mostly sensory and related to the degree of axonal damage at the level of an epineurotomy or perineurotomy is discussed.

Repair of Motor Nerve Gaps With Sensory Nerve Inhibits Regeneration in Rats

Objective: Sensory nerve grafts are often used to reconstruct injured motor nerves, but the consequences of such motor/sensory mismatches are not well studied. Sensory nerves have more diverse fiber distributions than motor nerves and may possess phenotypically distinct Schwann cells. Putative differences in Schwann cell characteristics and pathway architecture may negatively affect the regeneration of motor neurons down sensory pathways. We hypothesized that sensory grafts impair motor target reinnervation, thereby contributing to suboptimal outcomes. This study investigated the effect of motor versus sensory grafts on nerve regeneration and functional recovery.

Use of cold-preserved allografts seeded with autologous Schwann cells in the treatment of a long-gap peripheral nerve injury.

Background: Limitations in autogenous tissue have inspired the study of alternative materials for repair of complex peripheral nerve injuries. Cadaveric allografts are one potential reconstructive material, but their use requires systemic immunosuppression. Cold preservation (≥7 weeks) renders allografts devoid of antigens, but these acellular substrates generally fail in supporting regeneration beyond 3 cm. In this study, the authors evaluated the reconstruction of extensive nonhuman primate peripheral nerve defects using 7-week cold-preserved allografts repopulated with cultured autologous Schwann cells. Methods: Ten outbred Macaca fascicularis primates were paired based on maximal genetic disparity as measured by similarity index assay. A total of 14 ulnar nerve defects measuring 6 cm were successfully reconstructed using autografts (n = 5), fresh allografts (n = 2), cold-preserved allografts (n = 3), or cold-preserved allografts seeded with autogenous Schwann cells (n = 4). Recipient immunoreactivity was evaluated by means of enzyme-linked immunosorbent spot assay, and nerves were harvested at 6 months for histologic and histomorphometric analysis. Results: Cytokine production in response to cold-preserved allografts and cold-preserved allografts seeded with autologous Schwann cells was similar to that observed for autografts. Schwann cell–repopulated cold-preserved grafts demonstrated significantly enhanced fiber counts, nerve density, and percentage nerve (p < 0.05) compared with unseeded cold-preserved grafts at 6 months after reconstruction. Conclusions: Cold-preserved allografts seeded with autologous Schwann cells were well-tolerated in unrelated recipients and supported significant regeneration across 6-cm peripheral nerve defects. Use of cold-preserved allogeneic nerve tissue supplemented with autogenous Schwann cells poses a potentially safe and effective alternative to the use of autologous tissue in the reconstruction of extensive nerve injuries.

Motor neuron regeneration through end-to-side repairs is a function of donor nerve axotomy.

Background: Over the past decade, a growing body of literature has emerged supporting the use of end-to-side (terminolateral) neurorrhaphy for the treatment of selected peripheral nerve injuries. It remains unclear, however, whether injury to the donor nerve is necessary to achieve significant regeneration through such repairs. Methods: End-to-side repair was studied in a rodent model in which the terminal limb of a transected peroneal nerve was sutured to the lateral aspect of the tibial nerve. Twenty-eight Lewis rats were randomized to four groups of seven animals each corresponding to incrementally greater donor nerve injuries as follows: group 1, conventional end-to-side neurorrhaphy; group 2, end-to-side neurorrhaphy with proximal crush injury; group 3, end-to-side neurorrhaphy with neurotomy; and group 4, end-to-end repair of transected peroneal nerve (positive control). Results: At 12 weeks, retrograde labeling of cell bodies of the ventral horn demonstrated significant differences between experimental groups, with mean counts in group 4 (1237 ± 171) > group 3 (522 ± 204) > group 2 (210 ± 132) ≥ group 1 (126 ± 146). This association between nerve injury and motor neuron counts was closely mirrored in quantitative assessments of peripheral nerve regeneration and normalized wet muscle masses. Conclusions: These data support the hypothesis that donor nerve injury is a prerequisite for significant motor neuronal regeneration across end-to-side repairs. Motor neuron regeneration through end-to-side repairs is optimized by deliberate transection of donor nerve axons.

FK506 Rescues Peripheral Nerve Allografts in Acute Rejection

This study investigated the ability of the immunosuppressant FK506 to reverse nerve allograft rejection in progress. Eighty-four Buffalo rats received posterior tibial nerve grafts from either Lewis or Buffalo donor animals. Allografts were left untreated for either 7, 10, or 14 days before receiving daily subcutaneous FK506 injections (2 mg/kg). Time-matched control animals received either an isograft, an allograft with continuous FK506, or an allograft with no postoperative FK506 therapy. All animals underwent weekly evaluation of nerve function by walking track analysis. Experimental group animals were sacrificed either immediately prior to initiation of FK506 therapy (days 7, 10, or 14), after 2 weeks of immunosuppressive treatment, or 8 weeks postsurgery. Histomorphometric analysis, consisting of measurements of total number of nerve fibers, neural density, and percent of neural debris, demonstrated a statistically significant increase in regeneration in the isograft group relative to the untreated allograft group within 28 days of transplantation. Grafts harvested from animals receiving 2 weeks of FK506 after 7 or 10 days of rejection were histomorphometrically similar to time-matched isografts. By contrast, grafts from animals receiving 2 weeks of FK506 following 14 days without therapy resembled untreated allografts and demonstrated significant histomorphometric differences from isografts at the corresponding time point. Analysis of walking track data confirmed that relative to untreated allografts, functional recovery was hastened in animals receiving an isograft, or allograft treated with FK506. This study demonstrated that when started within 10 days of graft placement, FK506 could reverse nerve allograft rejection in rats evaluated following 2 weeks of treatment.