Hyperphosphorylation induces self-assembly of tau into tangles of paired helical filaments/straight filaments

The microtubule-associated protein tau is a family of six isoforms that becomes abnormally hyperphosphorylated and accumulates in the form of paired helical filaments (PHF) in the brains of patients with Alzheimer's disease (AD) and patients with several other tauopathies. Here, we show that the abnormally hyperphosphorylated tau from AD brain cytosol (AD P-tau) self-aggregates into PHF-like structures on incubation at pH 6.9 under reducing conditions at 35 degrees C during 90 min. In vitro dephosphorylation, but not deglycosylation, of AD P-tau inhibits its self-association into PHF. Furthermore, hyperphosphorylation induces self-assembly of each of the six tau isoforms into tangles of PHF and straight filaments, and the microtubule binding domains/repeats region in the absence of the rest of the molecule can also self-assemble into PHF. Thus, it appears that tau self-assembles by association of the microtubule binding domains/repeats and that the abnormal hyperphosphorylation promotes the self-assembly of tau into tangles of PHF and straight filaments by neutralizing the inhibitory basic charges of the flanking regions.

Multiple forms of phosphatase from human brain: isolation and partial characterization of affi-gel blue nonbinding phosphatase activities

Phosphatases extracted from a human brain were resolved into two main groups, namely affi-gel blue-binding phosphatases and affi-gel blue-nonbinding phosphatases. Affi-gel blue binding phosphatases were further separated into four different phosphatase activities, designated P1-P4, and described previously. In the present study we describe the affi-gel blue-nonbinding phosphatases which were separated into seven different phosphatase activities, designated P5-P11 by poly-(L-lysine)-agarose and aminohexyl Sepharose 4B chromatographies. These seven phosphatase activities were active toward nonprotein phosphoester. P7-P11 and to some extent P5 could also dephosphorylate a phosphoprotein. They displayed different enzyme kinetics. On the basis of activity peak, the apparent molecular mass as estimated by Sephadex G-200 column chromatography for P5 was 49 kDa; P6, 32 kDa; P7, 150 kDa; P8, 250 kDa; P9, 165 kDa; P10, 90 kDa and P11, 165 kDa. Immunoblot analysis indicated that P8-P11 may belong to PP2B family, whereas P7 may associate with PP2A. The phosphatases P7-P11 were found to be effective in the dephosphorylation of Alzheimer's disease abnormally hyperphosphorylated tau. The resulting dephosphorylated tau regained its activity in promoting the microtubule assembly, suggesting that P7-P11 might regulate the phosphorylation of tau protein in the brain.

Mechanism of neurofibrillary degeneration and pharmacologic therapeutic approach

Neurofibrillary degeneration is a key histopathological brain lesion of Alzheimer disease (AD) and related neurodegenerative disorders such as frontotemporal dementia and Parkinsonism linked to chromosome 17 (FTDP-17), commonly referred to as tauopathies. Microtubule associated protein (MAP) tau, which is a major MAP of a normal mature neuron is abnormally hyperphosphorylated in tauopathies and is the major protein subunit of paired helical filaments (PHF)/straight filaments (SF) which accumulate in the soma (as neurofibrillary tangles) and dystrophic neurites (as neuropil threads and as dystrophic neurites surrounding the beta-amyloid core in neuritic plaques in AD) of the affected neurons. Unlike normal tau which stimulates assembly and stabilizes microtubules, the abnormally hyperphosphorylated tau inhibits assembly and disrupts microtubules. The abnormally hyperphosphorylated tau competes with tubulin/microtubules in associating with normal tau, MAP1 and MAP2. This sequestration of normal MAPs by the abnormal tau results in the breakdown of the microtubules. The association of the abnormal tau with normal tau and not with MAP1 or MAP2 results in the formation of tangles of tau filaments. All these toxic properties of the abnormally hyperphosphorylated tau are eliminated by its enzymatic dephosphorylation. Activities of phosphoseryl/phosphothreonyl protein phosphatases (PP)-2A and PP-1 which can dephosphorylate the abnormal tau to a normal-like state are compromised in AD brain. Dephosphorylation by PP-2A and PP-2B and to a lesser extent by PP-1 restores the normal microtubule assembly promoting activity in AD P-tau in vitro. Neurofibrillary tangles of PHF isolated from AD brain are also dissociated on in vitro dephosphorylation with PP-2A, and the tau released by this treatment can stimulate microtubule assembly. Thus, it appears that the abnormal hyperphosphorylation of tau leads to neurodegeneration through breakdown of the microtubule network and that the abnormal tau on association with normal tau forms neurofibrillary tangles of tau filaments i.e. PHF/SF. Increase in tau phosphatase activity is a promising approach to inhibit neurofibrillary degeneration and thereby the diseases characterized by this lesion.

Inhibition of PP-2A upregulates CaMKII in rat forebrain and induces hyperphosphorylation of tau at Ser 262/356

The regulation of the activity of CaMKII by PP-1 and PP-2A, as well as the role of this protein kinase in the phosphorylation of tau protein in forebrain were investigated. The treatment of metabolically active rat brain slices with 1.0 microM okadaic acid (OA) inhibited approximately 65% of PP-2A and had no significant effect on PP-1 in the 16000xg tissue extract. Calyculin A (CL-A), 0.1 microM under the same conditions, inhibited approximately 50% of PP-1 and approximately 20% of PP-2A activities. In contrast, a mixture of OA and CL-A practically completely inhibited both PP-2A and PP-1 activities. The inhibition of the two phosphatase activities or PP-2A alone resulted in an approximately 2-fold increase in CaMKII activity and an approximately 8-fold increase in the phosphorylation of tau at Ser 262/356 in 60 min. Treatment of the brain slices with KN-62, an inhibitor of the autophosphorylation of CaMKII at Thr 286/287, produced approximately 60% inhibition in CaMKII activity and no significant effect on tau phosphorylation at Ser 262/356. The KN-62-treated brain slices when further treated with OA and CL-A did not show any change in CaMKII activity. In vitro, both PP-2A and PP-1 dephosphorylated tau at Ser 262/356 that was phosphorylated with purified CaMKII. These studies suggest (i) that in mammalian forebrain the cytosolic CaMKII activity is regulated mainly by PP-2A, (ii) that CaMKII is the major tau Ser 262/356 kinase in brain, and (iii) that a decrease in PP-2A/PP-1 activities in the brain leads to hyperphosphorylation of tau not only by inhibition of its dephosphorylation but also by promoting the CaMKII activity.

Metabolically active rat brain slices as a model to study the regulation of protein phosphorylation in mammalian brain

The reversible protein phosphorylation is the most important cellular regulation of the biological functions of many proteins. Disregulation of protein phosphorylation is involved in pathogeneses of several human diseases. The abnormal hyperphosphorylation of microtubule-associated protein tau and its aggregation into neurofibrillary tangles in selective neurons is one of the major brain pathologies of Alzheimer's disease and several other related neurodegenerative diseases. Here we present metabolically competent rat brain slices as a model to study the regulation of protein phosphorylation in brain. Employing this model we have been able to study the abnormal hyperphosphorylation of tau and other microtubule-associated proteins. We have evaluated the activity and intactness of the rat brain slices both biochemically and morphologically. Selective inhibition of protein phosphatase 2A in these rat brain slices by the treatment with okadaic acid induced hyperphosphorylation of tau at many abnormal sites seen in Alzheimer's disease brain and the accumulation of hyperphosphorylated tau in pyramidal neurons of the cortex and hippocampus. The regulation of the phosphorylation of high-molecular-weight microtubule-associated protein, MAP1b, was also studied with this model. This model enables studies on the regulation of protein phosphorylation not only biochemically, but also histochemically and immunocytochemically. Furthermore, unlike cultured cells, the neurons in the brain slices reside in the physiological environment of the brain consisting of natural extracellular matrix, neuronal connectivity, and neuronal-glial interactions.

Predicted region of stability for balance recovery: motion at the knee joint can improve termination of forward movement

Earlier experimental studies on balance recovery following perturbation have identified two discrete strategies commonly employed by humans, i.e. hip and ankle strategies. It has hence been implied that the knee joint plays a relatively minor role in balance recovery. The purpose of this study was to determine whether the size of the feasible stability region (FSR) would be affected by allowing knee motion in sagittal plane movement termination. The FSR was defined as the feasible range of anterior velocities of the center of mass (COM) of a human subject that could be reduced to zero with the final COM position within the base of support (BOS) limits. The FSR was computed using a four-segment biomechanical model and optimization routine based on Simulated Annealing algorithm for three scenarios: unrestricted knee motion (UK), restricted knee motion (RK), and unrestricted knee motion with an initial posture that matches RK (UKM). We found that movement termination could benefit little from UK condition when the COM (x(COM)) was initially located in the forefoot region [0.00 (toe) >x(COM)>/=-0.50 (mid-foot)] with no more than a 17% increase in FSR compared to RK. The effect of knee motion increased in the rear foot region with a 25% increase in FSR at x(COM)=-1 (heel). Close to half of this difference (12%) was attributable to the knee-related restriction on initial posture and the rest to movement termination per se. These findings illustrated a theoretical role of knee motion in standing humans' repertoire of effective posture responses, which include hip and ankle strategies and their variants for balance recovery with stationary BOS.

Role of protein phosphatase-2A and -1 in the regulation of GSK-3, cdk5 and cdc2 and the phosphorylation of tau in rat forebrain

In Alzheimer disease brain the activities of protein phosphatase (PP)-2A and PP-1 are decreased and the microtubule-associated protein tau is abnormally hyperphosphorylated at several sites at serine/threonine. Employing rat forebrain slices kept metabolically active in oxygenated artificial CSF as a model system, we investigated the role of PP-2A/PP-1 in the regulation of some of the major abnormally hyperphosphorylated sites of tau and the protein kinases involved. Treatment of the brain slices with 1.0 microM okadaic acid inhibited approximately 65% of PP-2A and produced hyperphosphorylation of tau at Ser 198/199/202, Ser 396/404 and Ser 422. No significant changes in the activities of glycogen synthase kinase-3 (GSK-3) and cyclin dependent protein kinases cdk5 and cdc2 were observed. Calyculin A (0.1 microM) inhibited approximately 50% PP-1, approximately 20% PP-2A, 50% GSK-3 and approximately 30% cdk5 but neither inhibited the activity of cyclin AMP dependent protein kinase A (PKA) nor resulted in the hyperphosphorylation of tau at any of the above sites. Treatment of brain slices with 1 microM okadaic acid plus 0.1 microM calyculin A inhibited approximately 100% of both PP-2A and PP-1, approximately 80% of GSK-3, approximately 50% of cdk5 and approximately 30% of cdc2 but neither inhibited PKA nor resulted in the hyperphosphorylation of tau at any of the above sites. These studies suggest (i) that PP-1 upregulates the phosphorylation of tau at Ser 198/199/202 and Ser 396/404 indirectly by regulating the activities of GSK-3, cdk5 and cdc2 whereas PP-2A regulates the phosphorylation of tau directly by dephosphorylation at the above sites, and (ii) that a decrease in the PP-2A activity leads to abnormal hyperphosphorylation of tau at Ser 198/199/202, Ser 396/404 and Ser 422.

Pulmonary function profile in chronic congestive heart failure and the effect of ipratropium bromide

Twenty-five symptomatic patients of chronic heart failure were subjected to spirometry to detect abnormalities of pulmonary function and to assess the effect of ipratropium bromide in reversing or minimising these abnormalities. All the patients exhibited abnormal pulmonary function manifesting as obstructive (15/25) or restrictive (10/25) ventilatory defect. There was overall improvement in lung functions with ipratropium bromide especially in those with obstructive ventilatory defects and mostly comprised of smokers. Forced expiratory volume in one second increased by 47.7 percent (p < 0.02), forced expiratory volume in one second/forced vital capacity ratio by 14.1 percent (p < 0.001) and maximal voluntary ventilation by 40.6 percent (p < 0.05) in these patients. It is concluded that ipratropium bromide can prove as a promising adjunctive therapeutic intervention in improving quality of life in patients of chronic congestive heart failure who are incapacitated by dyspnoea and have clearly documented ventilatory defects.

[Association of microtubule promoting and binding activity of tau with its phosphorylation sites]

OBJECTIVE

To explore the association between the abnormal phosphorylation sites found in Alzheimer disease (AD) tau and the inhibition of its biological activity.

METHODS

Ultracentrifugation, chromatography, manual Edman degradation and autosequence techniques were used to prepare and phosphorylate human recombinant tau, isolate and purify 32P tau peptides and determine phosphorylation sites.

RESULTS

(1) Phosphorylation of tau by casein kinase-1 (CK-1), cyclic AMP-dependent protein kinase (PKA) and glycogen synthetase kinase-3 (GSK-3) differentially inhibited its biological activity, and the inhibition of this activity of tau by GSK-3 was significantly increased if tau was prephosphorylated by CK-1 or PKA. The most potent inhibition was seen by a combined phosphorylation of tau with PKA and GSK-3. (2) The treatment of tau by PKA and GSK-3 combination induced phosphorylation of tau at Ser-195, Ser-198, Ser-199, Ser-202, Thr-205, Thr-231, Ser-235, Ser-262, Ser-356, Ser-404, whereas only Thr-181, Ser-184, Ser-262, Ser-356 and Ser-400 were phosphorylated by GSK-3 alone under the same conditions. Among the above-mentioned phosphorylation sites, Ser-198, Ser-199, Ser-202, Thr-205, Thr-231, Ser-235, Ser-262, Ser-400 and Ser-404 were seen in Alzheimer tau. The phosphorylation of Ser-262 only slightly inhibited its biological activity, and Ser-198, Ser-199, Ser-202, Thr-231, Ser-235, Ser-400 and Ser-404 also presented in fetal tau which was highly active, suggesting that Thr-205 was the unique site which both caused the potent inhibition of biological activity and specifically presented in AD abnormally phosphorylated tau.

CONCLUSIONS

Phosphorylation of Thr-205 might play a key role in tau pathology in AD.

Inactivation of glycogen synthase kinase-3 by protein kinase C delta: implications for regulation of tau phosphorylation

The role of the phosphatidylinositol 3-kinase (PI3K) pathway in the hyperphosphorylation of tau was investigated in SY5Y human neuroblastoma cells. Wortmannin, an inhibitor of PI3K, induced transient (after 1 h) activation of glycogen synthase kinase-3 (GSK-3), hyperphosphorylation of tau and dose-dependent cytotoxicity. However, continuous inactivation of protein kinase (PK) B was observed from 1 to 24 h, suggesting the involvement of protein kinase(s) other than PKB in the phosphorylation and inactivation of GSK-3 after 3 h. In cells treated with wortmannin, PKC delta fragments were observed, and the PKC activity increased after 3 h, whereas treatment of cells with z-DEVD-fmk, an inhibitor of caspase 3, also inhibited fragmentation of PKC delta and induced continuous activation of GSK-3. It is suggested that fragmentation of PKC delta during the process of apoptosis results in the phosphorylation and inactivation of GSK-3 and consequently inhibition of the phosphorylation of tau.

Thresholds for step initiation induced by support-surface translation: a dynamic center-of-mass model provides much better prediction than a static model

The need to initiate a step in order to recover balance could, in theory, be predicted by a static model based solely on displacement of the center of mass (COM) with respect to the base of support (BOS), or by a dynamic model based on the interaction between COM displacement and velocity. The purpose of this study was to determine whether the dynamic model provides better prediction than the static model regarding the need to step in response to moving-platform perturbation. The COM phase plane trajectories were determined for 10 healthy young adults for trials where the supporting platform was translated at three different acceleration levels in anterior and posterior directions. These trajectories were compared with the thresholds for step initiation predicted by the static and dynamic COM models. A single-link-plus-foot biomechanical model was employed to mathematically simulate termination of the COM movement, without stepping, using the measured platform acceleration as the input. An optimization routine was used to determine the stability boundaries in COM state space so as to establish the dynamic thresholds where a compensatory step must be initiated in order to recover balance. In the static model, the threshold for step initiation was reached if the COM was displaced beyond the BOS limits. The dynamic model showed substantially better accuracy than the static model in predicting the need to step in order to recover balance: 71% of all stepping responses predicted correctly by the dynamic model versus only 11% by the static model. These results support the proposition that the central nervous system must react to and control dynamic effects, i.e. COM velocity, as well as COM displacement in order to maintain stability with respect to the existing BOS without stepping.

Phosphorylation of microtubule-associated protein tau is regulated by protein phosphatase 2A in mammalian brain. Implications for neurofibrillary degeneration in Alzheimer's disease

Hyperphosphorylated tau, which is the major protein of the neurofibrillary tangles in Alzheimer's disease brain, is most probably the result of an imbalance of tau kinase and phosphatase activities in the affected neurons. By using metabolically competent rat brain slices as a model, we found that selective inhibition of protein phosphatase 2A by okadaic acid induced an Alzheimer-like hyperphosphorylation and accumulation of tau. The hyperphosphorylated tau had a reduced ability to bind to microtubules and to promote microtubule assembly in vitro. Immunocytochemical staining revealed hyperphosphorylated tau accumulation in pyramidal neurons in cornu ammonis and in neocortical neurons. The topography of these changes recalls the distribution of neurofibrillary tangles in Alzheimer's disease brain. Selective inhibition of protein phosphatase 2B with cyclosporin A did not have any significant effect on tau phosphorylation, accumulation, or function. These studies suggest that protein phosphatase 2A participates in regulation of tau phosphorylation, processing, and function in vivo. A down-regulation of protein phosphatase 2A activity can lead to Alzheimer-like abnormal hyperphosphorylation of tau.

Regulation of phosphorylation of neuronal microtubule-associated proteins MAP1b and MAP2 by protein phosphatase-2A and -2B in rat brain

The function of the neuronal high molecular weight microtubule-associated proteins (MAPs) MAP1b and MAP2 is regulated by the degree of their phosphorylation, which in turn is controlled by the activities of protein kinases and protein phosphatases (PP). To investigate the role of PP in the regulation of the phosphorylation of MAP1b and MAP2, we used okadaic acid and cyclosporin A to selectively inhibit PP2A and PP2B activities, respectively, in metabolically competent rat brain slices. The alteration of the phosphorylation levels of MAP1b and MAP2 was examined by Western blots using several phosphorylation-dependent antibodies to these proteins. The inhibition of PP2A, and to a lesser extent of PP2B, was found to induce an increased phosphorylation of MAP1b and inhibit its microtubule binding activity. Immunocytochemically, a marked increase in neuronal staining in inhibitor-treated tissue was observed with antibodies to the phosphorylated MAP1b. The inhibition of PP2A but not of PP2B also induced phosphorylation of MAP2 at multiple sites and impaired its microtubule binding activity. These results suggest that PP2A might be the major PP that participates in regulation of the phosphorylation of MAP1b and MAP2 and their biological activities.

Multiple forms of phosphatase from human brain: isolation and partial characterization of affi-gel blue binding phosphatases

Implication of protein phosphatases in Alzheimer disease led us to a systemic investigation of the identification of these enzyme activities in human brain. Human brain phosphatases eluted from DEAE-Sephacel with 0.22 M NaCl were resolved into two main groups by affi-gel blue chromatography, namely affi-gel blue-binding phosphatases and affi-gel blue-nonbinding phosphatases. Affi-gel blue-binding phosphatases were further separated into four different phosphatases, designated P1, P2, P3, and P4 by calmodulin-Sepharose 4B and poly-(L-lysine)-agarose chromatographies. These four phosphatases exhibited activities towards nonprotein phosphoester and two of them, P1 and P4, could dephosphorylate phosphoproteins. The activities of the four phosphatases differed in pH optimum, divalent metal ion requirements, sensitivities to various inhibitors and substrate affinities. The apparent molecular masses as estimated by gel-filtration for P1, P2, P3, and P4 were 97, 45, 42, and 125 kDa, respectively. P1 is markedly similar to PP2B from bovine brain and rabbit skeletal muscle. P4 was labeled with anti-PP2A antibody and may represent a new subtype of PP2A. P1 and P4 were also effective in dephosphorylating Alzheimer disease abnormally hyperphosphorylated tau (AD P-tau). The resulting dephosphorylated AD P-tau had its activity restored in promoting assembly of microtubules in vitro. These results suggest that P1 and P4 might be involved in the regulation of phosphorylation of tau in human brain, especially in neurodegenerative conditions like Alzheimer's disease which are characterized by the abnormal hyperphosphorylation of this protein.

Distribution of active glycogen synthase kinase 3beta (GSK-3beta) in brains staged for Alzheimer disease neurofibrillary changes

Accumulation of paired helical filaments (PHFs) in neurofibrillary tangles, neuropil threads, and dystrophic neurites is one of the major neuropathological hallmarks of Alzheimer disease (AD). The principal protein subunit of PHFs is the abnormally hyperphosphorylated tau. Glycogen synthase kinase 3beta (GSK-3beta) is one of the candidate kinases involved in PHF-tau formation. To play a role in PHF-tau formation, it would be expected that GSK-3beta is active in tangle bearing neurons. In the present study, we investigated the regional and intracellular distributions of active and inactive forms of GSK-3beta in brains staged for neurofibrillary changes. We found that neurons with tangle-like inclusions positive for active, but not inactive, GSK-3beta appear initially in the Pre-alpha layer of the entorhinal cortex and extend to other brain regions, coincident with the sequence of the development of neurofibrillary changes. Active, but not inactive, GSK-3beta was found to initially accumulate in the cytoplasm of pretangle neurons. These data provide direct in situ evidence that is consistent with the involvement of GSK-3beta in PHF-tau formation.

Immune response in acute coronary syndromes

Inflammatory response in the atherosclerotic lesions of coronary artery disease, mediated by cellular immune mechanisms is well appreciated. The significance of the immuno-inflammatory processes for the development of acute ischaemic sequelae of these lesions remains unsettled. Fifty patients of acute coronary syndromes were studied for complement components and immunoglobin levels by single radial immunodiffusion method. Twenty-eight patients of acute myocardial infarction showed significantly lower levels of complement components C3 and C4 at admission (C3--69.19 +/- 12.91 mg% compared to 82.40 +/- 9.26 mg% in controls, p < 0.01; C4--14.56 +/- 2.46 mg% compared to 18.53 +/- 2.69 mg% in controls, p < 0.01). Twenty-two patients of unstable angina did not show any significant change (C3--83.14 +/- 8.01 mg% and C4--19.07 +/- 4.47 mg%). Sixteen patients of acute myocardial infarction who were thrombolysed with streptokinase showed a steep rise in the levels of complement components immediately after thrombolysis (C3--69.19 +/- 12.91 mg% before and 100.56 +/- 17.09 mg% after thrombolysis, p < 0.001; C4--14.56 +/- 2.46 mg% before and 21.48 +/- 4.78 mg% after thrombolysis, p < 0.001). Plasma C3 and C4 levels in acute myocardial infarction showed no relationship with peak CPK levels. Plasma immunoglobulins remained unchanged in patients of acute coronary syndromes.

Regulation of expression, phosphorylation and biological activity of tau during differentiation in SY5Y cells

Tau, one of the best characterized microtubule-associated proteins (MAPs), is a phosphoprotein, the biological activity of which is regulated by its degree of phosphorylation. The objective of the present study was to evaluate the regulation, phosphorylation and the biological activity of tau during differentiation. On differentiation, the tau/tubulin ratio increased about 3-fold regardless whether cells were optimally differentiated with retinoic acid and aphidicolin or with retinoic acid alone which does not inhibit proliferation. The phosphorylation at the Tau-1 (Ser-195/Ser-198/Ser-199/Ser-202) and PHF-1 (Ser-396/Ser-404) sites was increased, mostly in the retinoic acid treated cells, whereas phosphorylation of tau at the 12E8 (Ser-262/Ser-356) epitope was decreased in both groups by approximately 60%. Phosphorylation at the 12E8 site is thought to be one of the most prominent factors affecting the biological activity of tau. However, the microtubule binding activity of tau increased only slightly upon differentiation. Furthermore, a large part of the tau that bound to taxol-stabilized microtubules was phosphorylated at all three sites indicating that these sites are not major sites determining the biological activity of tau. These data show that differentiation of SY5Y cells results in increased tau levels rather than dephosphorylation of tau to meet the additional need in tau's biological activity.

Simulated movement termination for balance recovery: can movement strategies be sought to maintain stability in the presence of slipping or forced sliding?

Slipping during various kinds of movement often leads to potentially dangerous incidents of falling. The purpose of this study was to determine whether there was evidence to support the theory that movement strategies could be used by individuals to regain stability during an episode of slipping and whether forced sliding from a moving platform accurately simulated the effect of slipping on stability and balance. A single-link-plus-foot biomechanical model was used to mathematically simulate base of support (BOS) translation and body segment rotation during movement termination in sagittal plane. An optimization routine was used to determine region of stability [defined at given COM locations as the feasible range of horizontal velocities of the center of mass (COM) of human subject that can be reduced to zero with respect to the BOS while still allowing the COM to traverse within the BOS limits]. We found some 30% overlap in the region of stability for slipping and non-slipping conditions. This finding supports the theory that movement strategies can be sought for restoring stability and balance even if slipping unexpectedly occurs. We also found that forced sliding produces effects on stability that are similar to those of slipping, indicated by over 50% overlap in the regions of stability for the two conditions. In addition, forced sliding has distinctive effects on stability, including a "shift" of the region of stability extended beyond the BOS in the direction of sliding. These findings may provide quantifiable guidance for balance training aimed at reducing fall incidents under uncertain floor surface conditions.

Silent myocardial ischemia and cardiac autonomic neuropathy in diabetics

OBJECTIVE

To evaluate the association of silent myocardial ischemia (SMI) with cardiac autonomic neuropathy in asymptomatic diabetic patients.

MATERIAL AND METHODS

Two hundred asymptomatic patients of diabetes mellitus were assessed for evidence of cardiac autonomic neuropathy. Of these, 30 (15 males, 15 females; mean age 44.7 +/- 8.8 years) were found to have cardiac autonomic neuropathy. Thirty (30) age and sex matched diabetic patients (mean age 42.4 +/- 7.6 years) who had no evidence autonomic neuropathy were included in the study as control group. Both the groups of patients were evaluated for SMI by 24 hour ambulatory electrocardiographic (ECG) monitoring.

RESULTS

Incidence of SMI was significantly higher in patients with autonomic neuropathy 12/30 (40%) compared to those without 3/30 (10%) p < 0.001. Duration of diabetes was more (13 +/- 1.59 years) in patients with autonomic neuropathy compared to the control group (8.66 +/- 1.55 years) p < 0.001. Serum cholesterol and triglyceride levels were significantly higher in patients with autonomic neuropathy in comparison to control group < 0.05 and < 0.01, respectively. There was no difference in the pattern of SMI in the two groups (p = N.S).

CONCLUSION

Cardiac autonomic neuropathy predisposes patients with diabetes mellitus to SMI. Twenty four hour ambulatory ECG monitoring provides useful diagnostic information in early detection and evaluation of SMI in asymptomatic diabetic patients.