Alpha-Synuclein Oligomers and Neurofilament Light Chain Predict Phenoconversion of Pure Autonomic Failure.

OBJECTIVE: To explore the role of alpha-synuclein (αSyn) oligomers and neurofilament light chain (NfL) in cerebrospinal fluid (CSF) of patients with pure autonomic failure (PAF) as markers of future phenoconversion to multiple system atrophy (MSA). METHODS: Well-characterized patients with PAF (n = 32) were enrolled between June 2016 and February 2019 at Mayo Clinic Rochester and followed prospectively with annual visits to determine future phenoconversion to MSA, Parkinson's disease (PD), or dementia with Lewy bodies (DLB). ELISA was utilized to measure NfL and protein misfolding cyclic amplification (PMCA) to detect αSyn oligomers in CSF collected at baseline. RESULTS: Patients were followed for a median of 3.9 years. Five patients converted to MSA, 2 to PD, and 2 to DLB. NfL at baseline was elevated only in patients who later developed MSA, perfectly separating those from future PD and DLB converters as well as non-converters. ASyn-PMCA was positive in all but two cases (94%). The PMCA reaction was markedly different in five samples with maximum fluorescence and reaction kinetics previously described in MSA patients; all of these patients later developed MSA. INTERPRETATION: αSyn-PMCA is almost invariably positive in the CSF of patients with PAF establishing this condition as α-synucleinopathy. Both NfL and the magnitude and reaction kinetics of αSyn PMCA faithfully predict which PAF patients will eventually phenoconvert to MSA. This finding has important implications not only for prognostication, but also for future trials of disease modifying therapies, allowing for differentiation of MSA from Lewy body synucleinopathies before motor symptoms develop. ANN NEUROL 2021;89:1212-1220.

Alpha-Synuclein Oligomers and Neurofilament Light Chain in Spinal Fluid Differentiate Multiple System Atrophy from Lewy Body Synucleinopathies.

OBJECTIVE: To explore the role of alpha-synuclein (αSyn) oligomers and neurofilament light chain (NFL) in cerebrospinal fluid (CSF) as markers of early multiple system atrophy (MSA) and to contrast findings with Lewy body synucleinopathies. METHODS: In a discovery cohort of well-characterized early MSA patients (n = 24) and matched healthy controls (CON, n = 14), we utilized enzyme-linked immunosorbent assay to measure NFL and protein misfolding cyclic amplification (PMCA) to detect αSyn oligomers in CSF. We confirmed findings in a separate prospectively enrolled cohort of patients with early MSA (n = 38), Parkinson disease (PD, n = 16), and dementia with Lewy bodies (DLB, n = 13), and CON subjects (n = 15). RESULTS: In the discovery cohort, NFL was markedly elevated in MSA patients, with perfect separation from CON. αSyn-PMCA was nonreactive in all CON, whereas all MSA samples were positive. In the confirmatory cohort, NFL again perfectly separated MSA from CON, and was significantly lower in PD and DLB compared to MSA. PMCA was again nonreactive in all CON, and positive in all but 2 MSA cases. All PD and all but 2 DLB samples were also positive for αSyn aggregates but with markedly different reaction kinetics from MSA; aggregation occurred later, but maximum fluorescence was higher, allowing for perfect separation of reactive samples between MSA and Lewy body synucleinopathies. INTERPRETATION: NFL and αSyn oligomers in CSF faithfully differentiate early MSA not only from CON but also from Lewy body synucleinopathies. The findings support the role of these markers as diagnostic biomarkers, and have important implications for understanding pathophysiologic mechanisms underlying the synucleinopathies. ANN NEUROL 2020;88:503-512.

Elimination of spurious absent sweat response in QSWEAT recordings.

INTRODUCTION: Forearm QSWEAT recordings are occasionally absent in females, likely due to high skin resistance. METHODS: We identified consecutive subjects with no sudomotor abnormalities but absent/markedly reduced QSWEAT forearm volume, and repeated QSWEAT at the same site after gentle abrasion. RESULTS: QSWEAT volumes were absent for 4 subjects and markedly reduced for the other 4 (median 0.01, IQR 0-0.03). After gentle skin abrasion, repeat volumes were significantly higher for all subjects and became normal in 7 of 8 subjects. DISCUSSION: Skin abrasion restores QSWEAT volumes in previously absent/markedly reduced site suggesting that skin preparation using abrasion is more effective.

Intrathecal administration of autologous mesenchymal stem cells in multiple system atrophy.

OBJECTIVE: This phase I/II study sought to explore intrathecal administration of mesenchymal stem cells (MSCs) as therapeutic approach to multiple system atrophy (MSA). METHODS: Utilizing a dose-escalation design, we delivered between 10 and 200 million adipose-derived autologous MSCs intrathecally to patients with early MSA. Patients were closely followed with clinical, laboratory, and imaging surveillance. Primary endpoints were frequency and type of adverse events; key secondary endpoint was the rate of disease progression assessed by the Unified MSA Rating Scale (UMSARS). RESULTS: Twenty-four patients received treatment. There were no attributable serious adverse events, and injections were generally well-tolerated. At the highest dose tier, 3 of 4 patients developed low back/posterior leg pain, associated with thickening/enhancement of lumbar nerve roots. Although there were no associated neurologic deficits, we decided that dose-limiting toxicity was reached. A total of 6 of 12 patients in the medium dose tier developed similar, but milder and transient discomfort. Rate of progression (UMSARS total) was markedly lower compared to a matched historical control group (0.40 ± 0.59 vs 1.44 ± 1.42 points/month, p = 0.004) with an apparent dose-dependent effect. CONCLUSIONS: Intrathecal MSC administration in MSA is safe and well-tolerated but can be associated with a painful implantation response at high doses. Compelling dose-dependent efficacy signals are the basis for a planned placebo-controlled trial. CLASSIFICATION OF EVIDENCE: This phase I/II study provides Class IV evidence that for patients with early MSA, intrathecal MSC administration is safe, may result in a painful implantation response at high doses, and is associated with dose-dependent efficacy signals.

Comparison of baroreflex sensitivity with a fall and rise in blood pressure induced by the Valsalva manoeuvre.

The baroreflex plays a key role in human BP (blood pressure) regulation. Its efferent limb consists of a vagal and a sympathetic component. The Valsalva manoeuvre is widely used to quantify vagal baroreflex function [BRS_vagal (vagal baroreflex sensitivity)], but most studies have focused on the R-R interval response to BP decrement, even though the subsequent response to an increment in BP is important and different. In the present study, we sought to evaluate whether BRS_vagal can be determined from BRSvagalinc (BRS_vagal derived from the rise in BP during phases III-IV of the Valsalva manoeuvre), to assess the association between BRSvagalinc and BRSvagaldec (BRS_vagal derived from the preceeding BP decrement) and to validate BRSvagalinc as an index of autonomic function. We studied patients with severe autonomic failure (n=49, 25 female), mild autonomic failure (n=25, 11 female) and matched normal controls (n=29, 15 female). BRSvagalinc and BRSvagaldec were calculated as the regression slope of R-R interval and systolic BP during phases III-IV and the early phase II of the Valsalva manoeuvre respectively, and compared these with other autonomic indices across the groups. BRSvagalinc was calculated in all subjects and correlated highly with BRSvagaldec (r=0.72, P<0.001). BRSvagalinc also correlated significantly with BP changes during phases II and IV of the Valsalva manoeuvre and sympathetic barosensitivity. BRSvagalinc was significantly different between the groups, being highest in the controls and lowest in patients with severe autonomic failure. In conclusion, vagal BRS, determined by relating R-R interval with the BP increase following phase III, is a valuable autonomic index, provides additional information about vagal baroreflex function and reflects overall severity of autonomic failure.

Effects of multiple injections of hypertonic dextrose in the rabbit carpal tunnel: a potential model of carpal tunnel syndrome development.

BACKGROUND: This study investigated the effects of a series of four hypertonic dextrose injections on the subsynovial connective tissue (SSCT) and median nerve within the carpal tunnel of a rabbit model. METHODS: Twenty New Zealand white rabbits were used. One forepaw carpal tunnel was randomly injected with 0.1 ml of 10 % dextrose solution. The contralateral forepaw was injected with a similar amount of saline. This injection was made once per week for 4 weeks. The animals were killed at 16 weeks after the initial injection and were evaluated by electrophysiology (EP), SSCT mechanical testing, and histology. RESULTS: Mechanical testing revealed significantly greater ultimate load and energy absorption in the dextrose injection group compared to the saline injection group (P < 0.05). Histological evaluation revealed SSCT fibrosis and thickening and edema in the median nerve bundles in the dextrose injection group. There was a prolongation in the latency of the EP test in the dextrose injection group (P = 0.08). CONCLUSIONS: Previous studies had shown that one or two injections of 10 % dextrose could induce moderate SSCT fibrosis and mild EP changes without nerve histology changes. In this study, we have shown that higher doses create more severe fibrosis and, most importantly, more severe neuropathy, suggesting a dose-response effect, and confirming this as a potentially useful animal model for researching the etiology and treatment of carpal tunnel syndrome.

Determination of vagal baroreflex sensitivity in normal subjects.

INTRODUCTION: The Valsalva maneuver (VM) is used widely to quantify the sensitivity of the vagal baroreflex loop (vagal baroreflex sensitivity, BRS_v), but most studies have focused on the heart rate (HR) response to blood pressure (BP) decrement (BRS_v↓), even though the subsequent response to an increment in BP after the VM (BRS_v↑) is important and different. METHODS: We evaluated recordings of HR and BP in 187 normal subjects during the VM and determined both BRS_v↑, as determined by relating HR to the BP increase after phase III and BRS_v↓. RESULTS: BRS_v↑ was related inversely to age. In addition, BRS_v↓, age, and magnitude of phase IV were independent predictors of BRS_v↑ in a multivariate model, accounting for 47% of the variance of BRS_v↑. CONCLUSIONS: The results indicate that both BRS_v↑ and BRS_v↓ become blunted with increasing age and that these indices relate to each other.

A novel and selective poly (ADP-ribose) polymerase inhibitor ameliorates chemotherapy-induced painful neuropathy.

BACKGROUND: Chemotherapy-induced neuropathy is the principle dose limiting factor requiring discontinuation of many chemotherapeutic agents, including cisplatin and oxaliplatin. About 30 to 40% of patients receiving chemotherapy develop pain and sensory changes. Given that poly (ADP-ribose) polymerase (PARP) inhibition has been shown to provide neuroprotection, the current study was developed to test whether the novel PARP inhibitor compound 4a (analog of ABT-888) would attenuate pain in cisplatin and oxaliplatin-induced neuropathy in mice. RESULTS: An established chemotherapy-induced painful neuropathy model of two weekly cycles of 10 intraperitoneal (i.p.) injections separated by 5 days rest was used to examine the therapeutic potential of the PARP inhibitor compound 4a. Behavioral testing using von Frey, paw radiant heat, cold plate, and exploratory behaviors were taken at baseline, and followed by testing at 3, 6, and 8 weeks from the beginning of drug treatment. CONCLUSION: Cisplatin-treated mice developed heat hyperalgesia and mechanical allodynia while oxaliplatin-treated mice exhibited cold hyperalgesia and mechanical allodynia. Co-administration of 50 mg/kg or 25 mg/kg compound 4a with platinum regimen, attenuated cisplatin-induced heat hyperalgesia and mechanical allodynia in a dose dependent manner. Similarly, co-administration of 50 mg/kg compound 4a attenuated oxaliplatin-induced cold hyperalgesia and mechanical allodynia. These data indicate that administration of a novel PARP inhibitor may have important applications as a therapeutic agent for human chemotherapy-induced painful neuropathy.

The effect of time after shear injury on the subsynovial connective tissue and median nerve within the rabbit carpal tunnel.

BACKGROUND: The most prominent nonneurological finding in the common compression neuropathy carpal tunnel syndrome (CTS) is fibrosis of the subsynovial connective tissue (SSCT). Recently, a rabbit model of CTS has been developed, based on the hypothesis that SSCT injury and subsequent fibrosis cause nerve compression. The purpose of this study was to evaluate the effects in this model at earlier and later time points than have heretofore been reported. METHODS: Sixty rabbits were operated on and observed at two different time periods: 6 and 24 weeks. Nerve electrophysiology (EP), SSCT histology, and SSCT mechanical properties were assessed. RESULTS: There was no significant difference in median motor nerve amplitude or latency at either time point. The total cell density in the SSCT was significantly higher at 6 and 24 weeks compared to controls. The mean size of the collagen fibrils in the SSCT was higher 6 and 24 weeks after surgery compared to controls. Both the ultimate load and the total energy absorption of the SSCT were significantly higher at 6 and 24 weeks compared to controls. CONCLUSIONS: In this model, there were signs of SSCT fibrosis and histology changes at 6 weeks, which persist after 24 weeks. Thus, this model leads to sustained SSCT fibrosis, which is one characteristic of human CTS. However, no significant EP changes were found at these two time points, which is in contrast to the findings reported previously for this model at 12 weeks. The significance of the differences in EP findings will be the subject of future studies.

Effects of hypertonic dextrose injections in the rabbit carpal tunnel.

OBJECTIVE: This study investigated the effects of different doses of hypertonic dextrose injection on the carpal tunnel subsynovial connective tissue (SSCT) and median nerve in a rabbit model. METHODS: Thirty-eight New Zealand white rabbits weighing 4.0-4.5 kg were used. One forepaw carpal tunnel was randomly injected with one of five different treatments: saline-single injection; saline-two injections 1 week apart; 10% dextrose-single injection; 20% dextrose-single injection; or 10% dextrose-two injections 1 week apart. Animals were sacrificed at 12 weeks after the initial injection and were evaluated by electrophysiology (EP), SSCT mechanical testing and histology. RESULTS: There were significant increases in the energy absorption of the SSCT in the 10% dextrose-double injection group compared to the saline injection groups. SSCT stiffness was also significantly increased in the 10% dextrose-double injection group compared to the other groups. There was a significant increase in the thickness of the SSCT in the 10% dextrose-double injection group compared to the saline-single injection group and a significant decrease in the nerve short-long diameter ratio in the 10% dextrose-double injection group compared to the saline-single injection group. There were no changes in EP among the groups. CONCLUSIONS: SSCT fibrosis is present for up to 12 weeks after dextrose injection; multiple injections have bigger effects, including what appears to be a secondary change in nerve flattening. This model may be useful to study the effects of external fibrosis on nerve morphology and physiology, such as occurs clinically in carpal tunnel syndrome.

Tendon injury produces changes in SSCT and nerve physiology similar to carpal tunnel syndrome in an in vivo rabbit model.

BACKGROUND: The etiology of carpal tunnel syndrome (CTS) remains idiopathic in many cases. Noninflammatory fibrosis of the subsynovial connective tissue (SSCT) within the carpal tunnel is common in CTS, and some clinicians have hypothesized that this fibrosis might be a cause rather than an effect of CTS. An animal model in which to test this hypothesis would be useful. The principal objective of this study was to investigate the effect of a surgical injury on SSCT fibrosis and median nerve function within the carpal tunnel in an in vivo rabbit model. METHODS: Rabbits were sacrificed 12 weeks after surgery and were evaluated by mechanical testing, histology, transmission and scanning electron microscopy, and electrophysiology. RESULTS: SSCT fibroblast density (p < 0.0001) and collagen fiber size (p = 0.0004) were significantly higher, and the median nerve distal motor amplitude was significantly lower (p = 0.0018), in the tendon injury group SSCT than in either the sham or control groups. CONCLUSIONS: Our findings are similar to those seen in patients with carpal tunnel syndrome and suggest that the tendon injury procedure may be the basis of a new animal model of SSCT injury and, possibly, CTS.

Ventilatory and cardiovascular responses to hypercapnia and hypoxia in multiple-system atrophy.

BACKGROUND: Loss of medullary sympathoexcitatory neurons may contribute to baroreflex failure, leading to orthostatic hypotension in multiple-system atrophy (MSA). The cardiovascular responses to chemoreflex activation in MSA have not been explored to date. OBJECTIVES: To determine whether ventilatory and cardiovascular responses to hypercapnia and hypoxia during wakefulness are systematically impaired in MSA. DESIGN: Case-control study. SETTING: Mayo Clinic, Rochester, Minnesota. PATIENTS: Sixteen patients with probable MSA (cases) and 14 age-matched control subjects (controls). MAIN OUTCOME MEASURES: Minute ventilation, blood pressure, and heart rate responses to hypercapnia and hypoxia during wakefulness. Hypercapnia was induced by a rebreathing technique and was limited to a maximal expiratory partial pressure of carbon dioxide of 65 mm Hg. Hypoxia was induced by a stepwise increase in inspiratory partial pressure of nitrogen and was limited to a minimal arterial oxygen saturation of 80%. Ventilatory responses were assessed as slopes of the regression line relating minute ventilation to changes in arterial oxygen saturation and partial pressure of carbon dioxide. RESULTS: In cases, ventilatory responses to hypercapnia and hypoxia were preserved, despite the presence of severe autonomic failure, while cardiovascular responses to these stimuli were impaired. Among cases, hypercapnia elicited a less robust increase in arterial pressure than among controls, and hypoxia elicited a depressor response rather than the normal pressor responses (P < .001 for both). CONCLUSIONS: Ventilatory responses to hypercapnia and hypoxia during wakefulness may be preserved in patients with MSA, despite the presence of autonomic failure and impaired cardiovascular responses to these stimuli. A critical number of chemosensitive medullary neurons may need to be lost before development of impaired automatic ventilation during wakefulness in MSA, whereas earlier loss of medullary sympathoexcitatory neurons may contribute to the impaired cardiovascular responses in these patients.

The effects of hypertonic dextrose injection on connective tissue and nerve conduction through the rabbit carpal tunnel.

OBJECTIVE: To investigate the effects of hypertonic dextrose injection on the subsynovial connective tissue (SSCT) in a rabbit model. We hypothesized that dextrose injection would induce proliferation of the SSCT, hinder median nerve conduction, and alter SSCT mechanical properties, similar to what is observed in patients with carpal tunnel syndrome (CTS). DESIGN: Randomized, controlled prospective study. SETTING: Not applicable. PARTICIPANTS: New Zealand white rabbits (N=28) weighing 4.0 to 4.5kg. INTERVENTION: One forepaw was randomly injected with 0.1mL 10% dextrose solution. The contralateral paw was injected with a similar amount of 0.9% saline solution as a control. Animals were killed at 12 weeks after injection. MAIN OUTCOME MEASURES: Animals were evaluated by electrophysiology (EP), mechanical testing, and histology. EP was evaluated by distal motor latency and amplitude. Shear force was evaluated when the middle digit flexor digitorum superficialis tendon was pulled out from the carpal tunnel. The ultimate tensile load and the energy absorption were also measured. Tissue for histology was evaluated qualitatively. RESULTS: EP demonstrated significant prolongation of distal motor latency. The energy absorption and stiffness were also significantly increased in the dextrose group. Histologically, the dextrose group showed thickening of the collagen bundles and vascular proliferation within the SSCT compared with the saline group. CONCLUSIONS: These results are consistent with the findings in patients with CTS and suggest that hypertonic dextrose injection has the potential to create a novel animal model in which to study the evolution of CTS.

Decreased peripheral nerve damage after ischemia-reperfusion injury in mice lacking TNF-alpha.

We sought to explore the role of tumor necrosis factor-alpha (TNF-alpha) in the pathogenesis of peripheral nerve ischemia-reperfusion (IR) injury. We established an ischemia-reperfusion model in wild type (WT) and TNF-alpha knockout (KO) mice. Electrophysiology, behavioral score and morphological indices (edema and ischemic fiber degeneration [IFD]) were examined to determine the influence of TNF-alpha on peripheral nerve structure and function following ischemia followed by reperfusion. TNF-alpha and nuclear factor-kappa B (NF-kappaB) expression were evaluated using immunohistochemistry. TNF-alpha KO mice, compared to WT had, in sciatic nerve, marked improvement in nerve pathology. This is a region subject to moderate ischemia-reperfusion injury. There was also a significant improvement in electrophysiological and some behavioral indices. TNF-alpha and NF-kappaB expression were abundant in sciatic-tibial nerves of WT mice subjected to IR, but there was less, or complete lack of, expression in ischemic nerve of TNF-alpha KO mice. We conclude that TNF-alpha plays an essential role in the pathogenesis of peripheral nerve ischemia-reperfusion injury, possibly partly through the activation of NF-kappaB.

Orchestration of the inflammatory response in ischemia-reperfusion injury.

Ischemia to nerve can cause fiber degeneration and reperfusion following ischemia [ischemia-reperfusion (IR)] adds the additional insult of an inflammatory response and oxidative injury. Limited information is available on the molecular mediators and their endoneurial targets. In this study, using a highly reproducible animal model of IR injury to nerve and selective immunolabeling methods [for nuclear factor kappa B (NF-kappaB), intercellular adhesion molecule-1 (ICAM-1), cytokines, and inflammatory cells] over an expanded time frame, we evaluated the temporal pattern and localization of mediators of the inflammatory response. Sixty rats were used. Nine groups (N=6 each) underwent complete hind limb ischemia for 4 h, followed by reperfusion durations of 0, 3, 12, 24, and 48 h, and 7, 14, 28, and 42 days. One group underwent sham operation (N=6). The earliest change was ICAM-1 expression in the microvessel (endothelial cell) followed almost immediately by NF-kappaB activation with axonal expression (24 and 48 h), followed by endoneurial edema and ischemic fiber degeneration (7 and 14 days). Granulocytic infiltration was followed by endoneurial infiltration of mononuclear phagocytes (14 days), expression of interleukin 6 (IL-6) (microvessels), and subsequent Schwann cell NF-kappaB expression. Granulocytes, tumor necrosis factor alpha, and IL-6-positive cells were observed primarily within the epineurium. IR results in changes in a number of interacting networks of targets and inflammatory mediators. NF-kappaB activation has a central orchestrating role involving both the axon and the Schwann cell in effecting the inflammatory response.

Multiple effects of hypothermia on inflammatory response following ischemia-reperfusion injury in experimental ischemic neuropathy.

Hypothermia is neuroprotective in peripheral nerve ischemia, but the mechanism(s) of neuroprotection are not well known. A major mechanism of ischemia-reperfusion (IR) injury is the inflammatory response. We therefore dissected the effects of hypothermia on inflammatory mediators in peripheral nerve ischemia of rats. Following functional and pathological evaluations for the effect of hypothermia on IR injury, we undertook immunohistochemical studies of inflammatory cells, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1), and nuclear factor kappa B (NF-kappaB) in nerve subjected to IR under defined hypothermic conditions with varying time delays (0, 1, 3, and 4 h) and depth of hypothermia (28 degrees C, 32 degrees C, and 35 degrees C). Functionally and pathologically, significant hypothermic neuroprotection was confirmed in the intraischemically treated groups but not in the postischemically treated groups. In endoneurial microvessels, intraischemic hypothermia inhibited ICAM-1 upregulation but not TNF-alpha, NF-kappaB, and IL-6 expressions. We demonstrated significantly reduced granulocyte and mononuclear phagocyte infiltration into nerve with intraischemic hypothermia but not with postischemic hypothermia. Cytokine (TNF-alpha and IL-6) positive cells were significantly decreased in both epineurium and endoneurium with intraischemic hypothermia. Excess NF-kappaB expression was seen in both Schwann cell and axon under normothermia (35 degrees C) but was inhibitable with deep hypothermia (28 degrees C). We conclude that intraischemic hypothermia significantly attenuates the inflammatory response by its effect on multiple key mediators including cytokines, ICAM-1, and NF-kappaB.

Enhanced inflammatory response via activation of NF-kappaB in acute experimental diabetic neuropathy subjected to ischemia-reperfusion injury.

Reperfusion following ischemia increases ischemic fiber degeneration (IFD) in diabetic nerves compared to control normoglycemic nerves. The mechanism of this excessive susceptibility is unclear. Since reperfusion injury results in an inflammatory response, we tested the hypothesis that the diabetic state increases the inflammatory cascade. We used an animal model of unilateral ischemia-reperfusion (IR) injury to streptozotocin (STZ)-induced diabetic nerve to evaluate the density and localization of mediators of the inflammatory response using selective immunolabeling methods (for nuclear factor kappa B (NF-kappaB), intercellular adhesion molecule-1 (ICAM-1), cytokines and inflammatory cells). We studied a 1-month diabetic group and an age-matched control group (n=6 each). The right limb underwent 3 h ischemia at 35 degrees C and 7 days reperfusion. This was achieved by ligating the supplying arteries and collaterals to the right sciatic-tibial nerve for 3 h, followed by releasing the ties. Immunohistochemistry was performed on proximal sciatic and mid tibial nerves. NF-kappaB expression in diabetic sciatic endothelial cell and Schwann cell (SC) was significantly increased over that of controls subjected to identical IR injury. We observed a nearly 2-fold increase in density of NF-kappaB and ICAM-1 expression in microvessels of diabetic nerve compared with control nerve. Extensive infiltration of monocyte macrophages (1C7) was observed in the endoneurium of diabetic nerves, while only mild infiltration of granulocytes (HIS 48) occurred in the endoneurium of diabetic tibial nerves. This study provides evidence for an enhanced inflammatory response in diabetic nerves subjected to IR injury apparently via NF-kappaB activation.

Ischemia-reperfusion injury causes oxidative stress and apoptosis of Schwann cell in acute and chronic experimental diabetic neuropathy.

Mild ischemia-reperfusion (IR) injury to diabetic peripheral nerve is known to cause severe ischemic fiber degeneration. Little information is available on its effects on Schwann cell (SC). In this study, we evaluated oxidative stress and apoptosis of SC following mild IR, using immunohistochemistry in streptozotocin (STZ)- induced diabetic rats. Twenty-six rats were divided into four groups according to the duration of diabetes: 1- month STZ-induced diabetic group (n=7) and age-matched control group (n=7); 4-month STZ-induced diabetic group (n=6) and age-matched control group (n=6). Using our established IR model of 3 h of ischemia followed by 7 days of reperfusion, sciatic and tibial nerves were harvested and labeled with 8-hydroxydeoxyguanosine (8-OHdG; oxidative stress marker), caspase-3 (apoptotic executor), and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) activity (apoptotic indicator). Marked positive staining with 8-OHdG, caspase-3, and TUNEL were found in diabetic ischemic nerves (right side) following IR in both 1-month and 4-month groups. Only mild positive staining or no staining was seen in the nonischemic side (left side) of diabetic and age-matched control groups. Co-labeling with S-100 confirmed that the cells labeled with 8-OHdG, caspase3, and TUNEL were SC. SC was susceptible to oxidative injury and apoptosis in experimental diabetic neuropathy when subjected to mild IR injury.

The therapeutic window of hypothermic neuroprotection in experimental ischemic neuropathy: protection in ischemic phase and potential deterioration in later reperfusion phase.

Hypothermia will neuroprotect peripheral nerve from ischemia-reperfusion (IR) injury, but the therapeutic window of hypothermic neuroprotection has not been defined. Unilateral IR injury was produced by the ligation and release of nooses tied around supplying arteries to the right sciatic-tibial nerve of the rat. Using this model, 114 rats were divided into 12 groups according to the delay (0, 1, 3, and 4 h) and the depth of hypothermia (28, 32, and 35 degrees C). All rats were subjected to 3 h ischemia and 7 days reperfusion followed by behavioral, electrophysiological, and pathological evaluations. We demonstrated significant hypothermic neuroprotection with both deep (28 degrees C) and mild (32 degrees C) hypothermia initiated during ischemia (0 and 1 h delay), but not hypothermia initiated during reperfusion (3 and 4 h delay) in both behavioral and electrophysiological evaluations. In addition, the pathologically significant differences were observed between deep hypothermia (28 degrees C) and normothermia (35 degrees C) initiated during ischemia. We conclude that the therapeutic window of hypothermic neuroprotection is optimal during the intraischemic period and that mild and deep hypothermia provide neuroprotection. Prolonged delay of hypothermic treatment results in worsening of IR injury.

Ischemia-reperfusion injury of peripheral nerve in experimental diabetic neuropathy.

The pathogenesis of human diabetic neuropathy likely involves the interplay of hyperglycemia, ischemia, and oxidative stress. Mild-moderate ischemia-reperfusion to streptozotocin (STZ)-induced diabetes results in florid fiber degeneration in diabetic but not in normal nerves. Uncertainty exists as to the influence of duration of diabetes on this susceptibility. We therefore studied diabetic tibial and sciatic nerves using a rat ischemia-reperfusion (IR) model after 1 month and 4 months of diabetes utilizing electrophysiological, behavioral, and neuropathological methods. Electrophysiological abnormalities were present in 1-month diabetic rats (D) and persisted over 4 months. Behavioral scores were decreased markedly at 4 months (p<0.05). Endoneurial edema and ischemia fiber degeneration (IFD) were observed at both the 1-month (p<0.01 and p<0.001) and 4-month (p<0.001) durations in diabetic nerves, whereas only mild or no damage was observed in age-matched control nerves. These findings demonstrate that STZ-induced diabetes exacerbates the morphological and electrophysiological pathology in peripheral nerve to IR injury both in the early timepoint of 1 month and late timepoint of 4 months, although there was a gradation of injury, which is more severe at the later timepoint. Reperfusion exaggerated morphological pathology in 1-month STZ-induced diabetic peripheral nerve.