Pain Attenuation through Mindfulness is Associated with Decreased Cognitive Control and Increased Sensory Processing in the Brain

Pain can be modulated by several cognitive techniques, typically involving increased cognitive control and decreased sensory processing. Recently, it has been demonstrated that pain can also be attenuated by mindfulness. Here, we investigate the underlying brain mechanisms by which the state of mindfulness reduces pain. Mindfulness practitioners and controls received unpleasant electric stimuli in the functional magnetic resonance imaging scanner during a mindfulness and a control condition. Mindfulness practitioners, but not controls, were able to reduce pain unpleasantness by 22% and anticipatory anxiety by 29% during a mindful state. In the brain, this reduction was associated with decreased activation in the lateral prefrontal cortex and increased activation in the right posterior insula during stimulation and increased rostral anterior cingulate cortex activation during the anticipation of pain. These findings reveal a unique mechanism of pain modulation, comprising increased sensory processing and decreased cognitive control, and are in sharp contrast to established pain modulation mechanisms.     

Increased Persistent Sodium Current Due to Decreased PI3K Signaling Contributes to QT Prolongation in the Diabetic Heart

Diabetes is an independent risk factor for sudden cardiac death and ventricular arrhythmia complications of acute coronary syndrome. Prolongation of the QT interval on the electrocardiogram is also a risk factor for arrhythmias and sudden death, and the increased prevalence of QT prolongation is an independent risk factor for cardiovascular death in diabetic patients. The pathophysiological mechanisms responsible for this lethal complication are poorly understood. Diabetes is associated with a reduction in phosphoinositide 3-kinase (PI3K) signaling, which regulates the action potential duration (APD) of individual myocytes and thus the QT interval by altering multiple ion currents, including the persistent sodium current I_NaP. Here, we report a mechanism for diabetes-induced QT prolongation that involves an increase in I_NaP caused by defective PI3K signaling. Cardiac myocytes of mice with type 1 or type 2 diabetes exhibited an increase in APD that was reversed by expression of constitutively active PI3K or intracellular infusion of phosphatidylinositol 3,4,5-trisphosphate (PIP3), the second messenger produced by PI3K. The diabetic myocytes also showed an increase in I_NaP that was reversed by activated PI3K or PIP3. The increases in APD and I_NaP in myocytes translated into QT interval prolongation for both types of diabetic mice. The long QT interval of type 1 diabetic hearts was shortened by insulin treatment ex vivo, and this effect was blocked by a PI3K inhibitor. Treatment of both types of diabetic mouse hearts with an I_NaP blocker also shortened the QT interval. These results indicate that downregulation of cardiac PI3K signaling in diabetes prolongs the QT interval at least in part by causing an increase in I_NaP. This mechanism may explain why the diabetic population has an increased risk of life-threatening arrhythmias.Patients with diabetes are at increased risk of developing life-threatening cardiac arrhythmias, independent of other risk factors such as atherosclerosis and hypertension. Diabetes is an independent risk factor for sudden cardiac death, mortality after myocardial infarction, and major complications of acute coronary syndrome such as ventricular arrhythmias (1). However, pathophysiological mechanisms responsible for the increased risk of sudden cardiac death remain poorly understood, and consequently there has been relatively little progress in the prevention and treatment of this diabetes complication. QT interval prolongation on the electrocardiogram (ECG) is a well-established risk factor for lethal ventricular arrhythmias (2), and not only do diabetic patients have a greater prevalence of QT interval prolongation than control populations (3,4), but a prolonged QT interval corrected for heart rate (QTc) is an independent risk factor for cardiovascular death in diabetic people (5–7).The signaling defect that causes QT interval prolongation in diabetes has remained elusive. An interesting lead came from our recent demonstration that decreased cardiac phosphoinositide 3-kinase (PI3K) signaling results in QT interval prolongation and is responsible for the increased risk of long QT syndrome and lethal arrhythmias caused by some anticancer drugs (8). Our results raised the possibility that suppression of this signaling pathway might also play a role in QT interval prolongation associated with diabetes, where reduced production of or sensitivity to insulin results in decreased activation of PI3K and its downstream effector, Akt.Primary prolongation of the QT interval (i.e., that which is independent of an altered QRS complex on the ECG) results from lengthening of the action potential duration (APD) in individual cardiac myocytes. The APD is regulated by inward and outward ion currents, and our previous study demonstrated that PI3K signaling regulates both types. PI3K inhibition caused reductions in the L-type calcium current (I_CaL), the delayed rectifier potassium currents I_Kr and I_Ks, and the peak sodium current (I_Na), whereas it caused an increase in the persistent (late) sodium current (I_NaP) (8). In the current study, we used mouse models to investigate a possible connection between decreased cardiac PI3K signaling and the prolonged QT interval in diabetes. Whereas I_Kr and I_Ks play little or no role in regulating the APD in adult mouse myocytes (9,10), I_NaP has a major role, such that expression of gain-of-function mutant sodium channels that increase I_NaP prolongs the murine APD and QT interval (11,12). Therefore, we used I_NaP as a marker of PI3K effects on cardiac ion channels and asked whether an increase in I_NaP contributes to QT interval prolongation in these diabetic mouse models.     

Increased Maternal Bone Formation in Type I Diabetic Pregnancies

There is evidence that infants of insulin-dependent diabetics have increased intrauterine bone resorption and reduced bone mineral content at birth. The aim of this study was to determine if type I diabetes is associated with abnormal maternal bone metabolism. We measured the circulating levels of carboxyterminal propeptide of type I procollagen (PICP) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP) in the third trimester of pregnancy in samples obtained from 19 pregnant women with type I diabetes and 19 pregnant controls, to monitor the rate of bone formation and degradation, respectively. Diabetic control was considered to be good as the mean hemoglobin A₁ level was less than 8.5%. The circulating levels of PICP were significantly higher in pregnant women with insulin-dependent diabetes than in controls with uncomplicated pregnancy (median IDDM 147 μg/liter, control 115 μg/liter, P= 0.0014), but there was no significant difference in the circulating levels of ICTP between the two groups (median IDDM 4.6 μg/liter, control 4.6 μg/liter, P= 0.907). Therefore, our findings suggest that there is an increase in bone formation in pregnant women with type I diabetes which may be related to the increased amount of insulin administered and the improvement in diabetic control associated with pregnancy. Received: 26 August 1998 / Accepted: 12 March 1999     

Protection of Sensory Function and Antihyperalgesic Properties of a Prosaposin-derived Peptide in Diabetic Rats

Background: Short-term diabetes causes sensory disorders in rats ranging from thermal hypoalgesia to exaggerated behavioral responses to other sensory stimuli. As impaired neurotrophic support may promote sensory nerve disorders during diabetes, the authors investigated whether TX14(A), a neurotrophic peptide derived from prosaposin, was able to ameliorate nerve disorders in diabetic rats.

Methods: TX14(A) was delivered by intraperitoneal or intrathecal injection to control or streptozotocin-diabetic rats in either single or multiple (three times weekly) dose regimens. Efficacy was measured against diabetes-induced disorders of sensory nerve conduction velocity, paw withdrawal latency to radiant heat, tactile response thresholds to von Frey filaments, and flinching after paw formalin injection.

Results: Prolonged TX14(A) treatment of diabetic rats prevented the progressive decline in large sensory fiber conduction velocity in the sciatic nerve, development of paw thermal hypoalgesia, and increased flinching after paw formalin injection. The effect on formalin hyperalgesia persisted for 48 h but not 72 h after injection. No effects were noted in control rats. A single injection of TX14(A) 30 min before testing did not alter thermal response latencies in control or diabetic rats but prevented formalin hyperalgesia in diabetic rats. Tactile allodynia and the prolonged paw thermal hyperalgesia to radiant heat after intrathecal delivery of substance P were also dose-dependently ameliorated in diabetic rats by a single injection of TX14(A), whereas no effects were observed on the responses to these tests in control rats.     

Increased Brain Lactate Concentrations Without Increased Lactate Oxidation During Hypoglycemia in Type 1 Diabetic Individuals

Previous studies have reported that brain metabolism of acetate is increased more than twofold during hypoglycemia in type 1 diabetic (T1D) subjects with hypoglycemia unawareness. These data support the hypothesis that upregulation of blood-brain barrier monocarboxylic acid (MCA) transport may contribute to the maintenance of brain energetics during hypoglycemia in subjects with hypoglycemia unawareness. Plasma lactate concentrations are ∼10-fold higher than acetate concentrations, making lactate the most likely alternative MCA as brain fuel. We therefore examined transport of [3-¹³C]lactate across the blood-brain barrier and its metabolism in the brains of T1D patients and nondiabetic control subjects during a hypoglycemic clamp using ¹³C magnetic resonance spectroscopy. Brain lactate concentrations were more than fivefold higher (P < 0.05) during hypoglycemia in the T1D subjects compared with the control subjects. Surprisingly, we observed no increase in the oxidation of blood-borne lactate in the T1D subjects, as reflected by similar ¹³C fractional enrichments in brain glutamate and glutamine. Taken together, these data suggest that in addition to increased MCA transport at the blood-brain barrier, there may be additional metabolic adaptations that contribute to hypoglycemia unawareness in patients with T1D.Despite the increased availability of improved methods for managing glycemic control (i.e., continuous glucose monitoring), failing counterregulation and hypoglycemia unawareness still present a real burden in the daily life of type 1 diabetic (T1D) and advanced (insulin-deficient) type 2 diabetic patients (1,2). Recurrent episodes of hypoglycemia are considered to induce both the failure in counterregulatory hormone release and hypoglycemia unawareness, a concept known as hypoglycemia-associated autonomic failure (3,4).Although the exact mechanisms of hypoglycemia unawareness are still unknown, studies have predominantly focused on adaptations related to nutrient transport into the brain and changes in brain energy metabolism. For example, changes in the transport of plasma glucose across the blood-brain barrier and consequently the brain glucose levels have been the topic of various studies (5–10). Other studies have focused on glycogen supercompensation, a hypothesis suggesting increased storage of glucose in astroglial glycogen after recurrent hypoglycemic events (11–13). The increased astroglial glycogen would function as a glucose reserve during hypoglycemia. However, during a 50-h wash-in and wash-out study of [1-¹³C]glucose, control subjects showed higher levels of newly synthesized brain glycogen than hypoglycemia-unaware T1D subjects (11). Öz et al. (11) consequently concluded that glycogen supercompensation did not contribute to hypoglycemia unawareness in T1D patients.Previously we have reported that brain transport and metabolism of acetate is increased more than twofold in intensively treated T1D subjects with hypoglycemia unawareness (14). These data support the hypothesis that upregulation of blood-brain barrier monocarboxylic acid (MCA) transport via MCA transporter 1 (15,16) may be a hallmark of hypoglycemia unawareness in T1D patients. In contrast to acetate, which circulates in plasma at relatively low concentrations (∼0.1 mmol/L), plasma lactate concentrations are ∼10-fold higher during hypoglycemia (17), making it a primary candidate for an alternative brain fuel (18–21).Lactate metabolism can play a central role in neuroenergetics, as suggested by the astrocyte-neuron lactate shuttle (22). The astrocyte-neuron lactate shuttle models the compartmentalized metabolism of glucose in astrocytes and neurons. It describes how glucose is metabolized through glycolysis in astrocytes, producing lactate. Lactate is then shuttled to neighboring neurons where it is oxidized. The astrocyte-neuron lactate shuttle is analogous to the intercellular lactate shuttle that was proposed earlier and describes skeletal muscle lactate metabolism (23).We have shown in healthy subjects that there is sufficient lactate transport activity to supply ∼10% of the brain’s energy needs at physiological lactate concentrations (24). Increased blood-brain barrier transport capacity of MCAs, and thus lactate, could contribute to the maintenance of brain energetics during hypoglycemia, providing the brain with an increased influx of alternative substrates (14). However, to our knowledge, there is no direct evidence of increased brain transport and oxidation of plasma lactate in T1D patients. We therefore examined transport of lactate over the blood-brain barrier and its metabolic fate in healthy T1D patients and nondiabetic control subjects during a hypoglycemic clamp by measuring ¹³C label incorporation from intravenously administered [3-¹³C]lactate into brain lactate, glutamate (Glu), and glutamine (Gln) by ¹³C magnetic resonance spectroscopy (MRS).     

血浆活化蛋白C与2型糖尿病肾病患者动脉粥样硬化的相关性

目的：探讨活化蛋白C（APC）与2型糖尿病肾病（DKD）患者动脉粥样硬化的关系。方法：ELISA方法检测41例2型糖尿病肾病患者和27位对照组志愿者的血浆APC水平,颈动脉超声测量颈动脉内中膜厚度（IMT）作为全身动脉粥样硬化的衡量指标。结果：与对照组相比,2型糖尿病肾病患者的血浆APC水平显著性降低[（10389.0±1801.9）vs（6693.3±1790.5）ng/ml,P〈0.001]。单因素相关分析显示,2型糖尿病肾病非透析患者的颈动脉IMT与血浆APC水平（r=-0.511,P〈0.01）负相关。多元逐步线性回归分析显示APC是平均颈动脉IMT的显著性相关因素（β=-0.492,P〈0.01）,且24h尿白蛋白排泄率（β=-0.719,P〈0.05）、血红蛋白（β=0.522,P〈0.05）是血浆APC水平的显著性相关因素。结论：APC的减少可能与2型糖尿病肾病患者的动脉粥样硬化相关,并可能在其动脉粥样硬化的病理过程中发挥作用。     

Time Sequence of Sensory Changes after Upper Extremity Block: Swelling Sensation Is an Early and Accurate Predictor of Success

Background: Sensory assessment to estimate spread and effectiveness of a peripheral nerve block is difficult because no clinical test is specific for small sensory fibers. Occurrence of a swelling illusion (SI) during a peripheral nerve block corresponds to the impairment of small sensory fibers. The authors investigated the usefulness of SI in predicting successful peripheral nerve block by assessing the temporospatial correlation between progression of sensory impairment in cutaneous distributions anesthetized and localization of SI during peripheral nerve block installation.

Methods: Interscalene, infracoracoid, or sciatic nerve blocks were performed using a nerve stimulator and 1.5% mepivacaine in 53 patients, with a total of 201 nerves to be anesthetized. Pinprick, cold, warm, touch, and proprioception were assessed every 3 min, while patients were asked to describe their perception of size and shape of their anesthetized limb and localization of these illusions. Data are presented as mean +/- SD and percentage (95% confidence interval).

Results: Failure occurred in 12 cutaneous distributions out of a total of 201 theoretically blocked nerves. SI appeared earlier than warmth impairment (4.3 +/- 2.7 vs. 6.2 +/- 2.0 min; P < 0.05), always corresponding to successfully anesthetized cutaneous distributions, with the exception of 1 patient, who developed SI in 2 cutaneous distributions while sensory testing indicated failure in 1 distribution. SI successfully predicted the blockade of a cutaneous distribution with a sensitivity of 1.00 (0.98-1.00), a specificity of 0.92 (0.65-0.99), and an accuracy of 0.99 (0.97-1.00).     

Increased Vitreous Shedding of Microparticles in Proliferative Diabetic Retinopathy Stimulates Endothelial Proliferation

OBJECTIVE

Diabetic retinopathy is associated with progressive retinal capillary activation and proliferation, leading to vision impairment and blindness. Microparticles are submicron membrane vesicles with biological activities, released following cell activation or apoptosis. We tested the hypothesis that proangiogenic microparticles accumulate in vitreous fluid in diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Levels and cellular origin of vitreous and plasma microparticles from control (n = 26) and diabetic (n = 104) patients were analyzed by flow cytometry, and their proangiogenic activity was assessed by in vitro thymidine incorporation and neovessel formation in subcutaneous Matrigel plugs in mice.

RESULTS

Microparticles of endothelial, platelet, photoreceptor, and microglial origin were identified in vitreous samples. Levels of photoreceptor and microglial microparticles were undetectable in plasmas but were comparable in diabetic and control vitreous samples. Vitreous platelet and endothelial microparticles levels were increased in diabetic patients and decreased following panretinal laser photocoagulation or intravitreal antivascular endothelial growth factor injection in proliferative diabetic retinopathy (PDR). The ratio of vitreous to plasma microparticle levels was calculated to estimate local formation versus potential plasma leakage. In PDR, the endothelial microparticles ratio—but not that for platelet—was greater than 1.0, indicating local formation of endothelial microparticles from retinal vessels and permeation of platelet microparticles from plasma. Isolated vitreous microparticles stimulated by 1.6-fold endothelial proliferation and increased new vessel formation in mice.

CONCLUSIONS

The present study demonstrates that vitreous fluid contains shed membrane microparticles of endothelial, platelet, and retinal origin. Vitreous microparticles levels are increased in patients with diabetic retinopathy, where they could contribute to disease progression.Despite advances in medical care, diabetic retinopathy continues to be a leading cause of vision impairment and blindness in working-age adults (1). The pathogenesis of diabetic retinopathy is complex and has involved multiple pathways including accumulation of polyol compounds and advanced glycation end products, increased oxidation stress and activation of the protein kinase C pathway, production of growth factors, and inflammation (1). Although there is growing evidence for an early involvement of the neural elements of the retina (2), vision loss in diabetic retinopathy is associated with progressive alterations of the retinal vasculature, leading to the breakdown of the blood retinal barrier and pathological angiogenesis of new vessels in the vitreous cavity (1,3). The risk of vision loss results then from macular edema and bleeding of these new vessels (vitreous hemorrhage) or their contraction (retinal detachment).Microparticles are submicron membrane vesicles shed from the cell surface of both healthy and damaged cells (4). Shedding of membrane microparticles is a physiological process that accompanies cell growth and activation and that is enhanced by cytokines, reactive oxygen species, activation of apoptotic pathways, or increases in intracellular calcium leading to cytoskeleton reorganization. Numerous studies now indicate that microparticles have biological activities and may be involved in thrombosis, cell inflammation, angiogenesis and cell-to-cell communication (5–12).Microparticles have been identified not only in human plasma but also in other tissues with high cellular activation, inflammation, or apoptosis, such as human atherosclerotic plaques or synovial fluid in rheumatoid arthritis (13,14). Plasma microparticles from different cellular origins circulate in healthy subjects, and their levels increase in patients with cardiovascular disease (15,16). The question of changes in circulating levels of microparticles appears to be controversial in diabetic patients (17,18), but plasma levels of platelet-derived and monocyte-derived microparticles increase with the severity of diabetic retinopathy (19,20).Diabetic retinopathy is associated with increased local activation or apoptosis of retinal, neural, and vascular endothelial cells in the eye both in humans and in animal models (21–24). These finding indicate that microparticles of different cellular origin might be locally generated in the eye of diabetic patients. Alternatively, the presence of microparticles in the eye could also result from an increased vascular permeability associated with diabetic retinopathy. Thus, we sought to investigate the presence of endothelial, platelet, and retinal-derived microparticles both in the vitreous and in the plasma of diabetic patients undergoing vitrectomy for diabetic retinopathy compared with that of nondiabetic patients. We also examined the potential biological effects of vitreous microparticles on endothelial proliferation and new vessel formation.     

Endothelin-1 and Endothelin A Receptor Immunoreactivity Is Increased in Patients with Diabetic Nephropathy

Background: Endothelin-1 (ET-1) is associated with progression of renal disease, acting as a vasoconstrictor and growth factor for mesangial cells. ET-1 and endothelin A receptor (ET-RA) might have a role in the development of diabetic nephropathy (DN). The aims of this study were to determine ET-1 and ET-RA expressions in patients with DN and to correlate these expressions with renal function and proteinuria. Materials and methods: This is a cross-sectional study comprising 13 patients with type 2 diabetes mellitus and DN, 10 patients with proteinuric IgA nephropathy, and 13 samples of normal kidney from tumor nephrectomies. Demographic and selected data were collected from medical charts. The distribution and intensity of ET-1 and ET-RA immunostaining in renal biopsies were determined by immunohistochemistry and these correlated with the estimated glomerular filtration rate (eGFR) and proteinuria. Results: Patients with DN and IgA nephropathy on biopsy had markedly increased staining for ET-1 in endothelial cells of glomerular and peritubular capillaries when compared with controls (p < 0.001). ET-RA staining was also more intense and more diffuse in DN and IgA nephropathy than in controls (p = 0.019) and was restricted to tubular epithelial cells. A positive correlation was observed between ET-1 expression and proteinuria (r = 0.634, p = 0.027), but both ET-1 and ET-RA expressions did not correlate with eGFR. Conclusion: In this preliminary report, the higher expressions of ET-1 and ET-RA found in both DN and IgA nephropathy suggest a potential role for the endothelin system in DN as well as in other nondiabetic glomerular diseases.     

Ileal Glucose Infusion Leads to Increased Insulin Sensitivity and Decreased Blood Glucose Levels in Wistar Rats

ABSTRACT

Purpose of the study: Rerouting of nutrients and/or increasing nutrient delivery to the small intestine after Roux-en-Y gastric bypass may have important potential as a diabetes treatment modality. However, it is still important question which part of the gastrointestinal tract is the most important for control of glycemia. The aim of this study was to investigate the role of different segments of the gastrointestinal tract on glucose metabolism in the physiological state. Materials and Methods: Forty 12-week-old male Wistar rats were divided into the following four groups of 10 animals each: the gastrostomy group, the duodenostomy group, the jejunostomy group, and the ileostomy group. All rats were subjected to a glucose tolerance test by infusion of glucose via the surgically inserted tubes in the stomach (gastrostomy), in the duodenum (duodenostomy), in the jejunum (jejunostomy), or in the ileum (ileostomy). Plasma glucagon-like peptide-1_7–36 (GLP-1_7–36) and insulin levels during the glucose tolerance test were assayed and Matsuda index was calculated. Results: Ileostomy rats exhibited significantly lower glycemic excursions compared with gastrostomy, duodenostomy, and jejunostomy rats. Insulin and GLP-1 levels during the glucose tolerance test were significantly higher in duodenostomy and jejunostomy rats than in gastrostomy and ileostomy rats. Matsuda index was significantly higher in ileostomy rats than in duodenostomy and jejunostomy rats. Conclusion: Ileal glucose infusion leads to increased insulin sensitivity, further decreasing blood glucose levels.     

FOXO1-Mediated Downregulation of RAB27B Leads to Decreased Exosome Secretion in Diabetic Kidneys

Exosomes have been implicated in diabetic kidney disease (DKD), but the regulation of exosomes in DKD is largely unknown. Here, we have verified the decrease of exosome secretion in DKD and unveiled the underlying mechanism. In Boston University mouse proximal tubule (BUMPT) cells, high-glucose (HG) treatment led to a significant decrease in exosome secretion, which was associated with specific downregulation of RAB27B, a key guanosine-5′-triphosphatase in exosome secretion. Overexpression of RAB27B restored exosome secretion in HG-treated cells, suggesting a role of RAB27B downregulation in the decrease of exosome secretion in DKD. To understand the mechanism of RAB27B downregulation, we conducted bioinformatics analysis that identified FOXO1 binding sites in the Rab27b gene promoter. Consistently, HG induced phosphorylation of FOXO1 in BUMPT cells, preventing FOXO1 accumulation and activation in the nucleus. Overexpression of nonphosphorylatable, constitutively active FOXO1 led to the upregulation of RAB27B and an increase in exosome secretion in HG-treated cells. In vivo, compared with normal mice, diabetic mice showed increased FOXO1 phosphorylation, decreased RAB27B expression, and reduced exosome secretion. Collectively, these results unveil the mechanism of exosome dysfunction in DKD where FOXO1 is phosphorylated and inactivated in DKD, resulting in RAB27B downregulation and the decrease of exosome secretion.     

Increased Hip Stresses Resulting From a Cam Deformity and Decreased Femoral Neck-Shaft Angle During Level Walking

Background

It is still unclear why many individuals with a cam morphology of the hip do not experience pain. It was recently reported that a decreased femoral neck-shaft angle may also be associated with hip symptoms. However, the effects that different femoral neck-shaft angles have on hip stresses in symptomatic and asymptomatic individuals with cam morphology remain unclear.

Questions/purposes

We examined the effects of the cam morphology and femoral neck-shaft angle on hip stresses during walking by asking: (1) Are there differences in hip stress characteristics among symptomatic patients with cam morphology, asymptomatic individuals with cam morphology, and individuals without cam morphology? (2) What are the effects of high and low femoral neck-shaft angles on hip stresses?

Methods

Six participants were selected, from a larger cohort, and their cam morphology and femoral neck-shaft angle parameters were measured from CT data. Two participants were included in one of three groups: (1) symptomatic with cam morphology; (2) asymptomatic with a cam morphology; and (3) asymptomatic control with no cam morphology with one participant having the highest femoral neck-shaft angle and the other participant having the lowest in each subgroup. Subject-specific finite element models were reconstructed and simulated during the stance phase, near pushoff, to examine maximum shear stresses on the acetabular cartilage and labrum.

Results

The symptomatic group with cam morphology indicated high peak stresses (6.3–9.5 MPa) compared with the asymptomatic (5.9–7.0 MPa) and control groups (3.8–4.0 MPa). Differences in femoral neck-shaft angle influenced both symptomatic and asymptomatic groups; participants with the lowest femoral neck-shaft angles had higher peak stresses in their respective subgroups. There were no differences among control models.

Conclusions

Our study suggests that the hips of individuals with a cam morphology and varus femoral neck angle may be subjected to higher mechanical stresses than those with a normal femoral neck angle.

Clinical Relevance

Individuals with a cam morphology and decreased femoral neck-shaft angle are likely to experience severe hip stresses. Although asymptomatic participants with cam morphology had elevated stresses, a higher femoral neck-shaft angle was associated with lower stresses. Future research should examine larger amplitudes of motion to assess adverse subchondral bone stresses.

     

Development of Selective Axonopathy in Adult Sensory Neurons Isolated From Diabetic Rats: Role of Glucose-Induced Oxidative Stress

OBJECTIVE

Reactive oxygen species (ROS) are pro-oxidant factors in distal neurodegeneration in diabetes. We tested the hypothesis that sensory neurons exposed to type 1 diabetes would exhibit enhanced ROS and oxidative stress and determined whether this stress was associated with abnormal axon outgrowth.

RESEARCH DESIGN AND METHODS

Lumbar dorsal root ganglia sensory neurons from normal or 3- to 5-month streptozotocin (STZ)-diabetic rats were cultured with 10 or 25–50 mmol/l glucose. Cell survival and axon outgrowth were assessed. ROS were analyzed using confocal microscopy. Immunofluorescent staining detected expression of manganese superoxide dismutase (MnSOD) and adducts of 4-hydroxy-2-nonenal (4-HNE), and MitoFluor Green dye detected mitochondria.

RESULTS

Dorsal root ganglion neurons from normal rats exposed to 25–50 mmol/l glucose did not exhibit oxidative stress or cell death. Cultures from diabetic rats exhibited a twofold (P < 0.001) elevation of ROS in axons after 24 h in 25 mmol/l glucose compared with 10 mmol/l glucose or mannitol. Perikarya exhibited no change in ROS levels. Axonal outgrowth was reduced by approximately twofold (P < 0.001) in diabetic cultures compared with control, as was expression of MnSOD. The antioxidant N-acetyl-cysteine (1 mmol/l) lowered axonal ROS levels, normalized aberrant axonal structure, and prevented deficits in axonal outgrowth in diabetic neurons (P < 0.05).

CONCLUSIONS

Dorsal root ganglia neurons with a history of diabetes expressed low MnSOD and high ROS in axons. Oxidative stress was initiated by high glucose concentration in neurons with an STZ-induced diabetic phenotype. Induction of ROS was associated with impaired axonal outgrowth and aberrant dystrophic structures that may precede or predispose the axon to degeneration and dissolution in human diabetic neuropathy.Diabetic sensory polyneuropathy in humans and animal models is associated with a spectrum of structural changes in peripheral nerves that includes microangiopathy, axonal degeneration, segmental demyelination, and ultimately loss of both myelinated and unmyelinated fibers (1,2). It has been proposed that high glucose concentrations induce toxicity and cell death in sensory neurons, and this triggers diabetic neuropathy through loss of nerve fibers (3). Cultured embryonic dorsal root ganglion sensory neurons were exposed to high nonphysiological concentrations of glucose that induced oxidative stress by increasing production of reactive oxygen species (ROS), and this was associated with mitochondrial dysfunction, which resulted in programmed cell death (4–6).Morphologic studies have provided a variety of results in relation to sensory neuron survival in animal models of diabetes. Long-term studies of 9 months in streptozotocin (STZ)-diabetic mice revealed a significant loss of sensory neurons (7). In STZ-diabetic rats of up to 12 months'' duration, no significant loss of adult lumbar dorsal root ganglion neurons was observed (8,9). Additionally, in 4-month diabetic BB rats, there was no dorsal root ganglion sensory neuron cell death (10); however, by 10 months there was progressive neuronal loss, but prominent only in the small dorsal root ganglion neuron population and not involving apoptosis (11). At the same time there was a significant decrease in the numbers of myelinated and unmyelinated fibers, but no evidence of structural changes in mitochondria in dorsal root ganglion sensory neurons (11). In STZ-diabetic mice, where loss of small neurons was also occurring, there was no sign of activation of the pro-apoptotic markers p38, caspase-3, and phosphorylated c-jun (12).Sural nerves from humans with diabetic neuropathy assessed using quantitative morphometry have significant endoneurial microangiopathy, early structural abnormalities in Schwann cells in myelinated fibers, and degeneration and loss of unmyelinated and myelinated fibers; however, in intact axons, mitochondria appeared structurally normal (1,13). In addition, studies performed on postmortem samples from type 2 diabetic patients have shown the occurrence of dystrophic changes in axon terminals and within the dorsal root ganglion and autonomic ganglia, but no evidence for significant neuronal cell loss (14,15).These results show that in vivo in animals and humans, the impact of diabetes on sensory neuron survival are discordant with the in vitro studies demonstrating toxic effects of high glucose concentration leading to apoptosis. We hypothesized that the underlying reason for this discrepancy was the use of embryonic sensory neurons for in vitro glucose toxicity studies (3). Cultured embryonic sensory neurons have phenotypic differences with adult sensory neurons and are dependent on neurotrophic factor–derived support for survival (16). Therefore, the aim of this study was to compare responses of adult dorsal root ganglion sensory neurons from age-matched control and 3- to 5-month STZ-diabetic rats exposed to high glucose concentration. To this end, the effect of high glucose concentration on oxidative stress and neuronal survival and axonal morphology was assessed.