Koon-Ho Chan

ANNA-3 anti-neuronal nuclear antibody: Marker of lung cancer-related autoimmunity

Two anti‐neuronal nuclear antibodies (ANNA‐1 and ANNA‐2) are markers of paraneoplastic neurological autoimmunity related to small‐cell carcinoma. ANNA‐2 is also related to breast carcinoma. Here we define a third IgG specificity (ANNA‐3), identified in 11 patients (10 adults) by immunofluorescence screening of sera from approximately 68,000 patients with suspected paraneoplastic neurological syndromes. ANNA‐3 binds prominently to nuclei of cerebellar Purkinje neurons, not to cytoplasm, granular neurons, or enteric neurons, but distinctively to renal glomerular podocytes. Western blots revealed an approximately 170 kDa antigen, in cerebellum and small‐cell carcinoma. IgG eluted from this protein reproduced Purkinje and podocyte nuclear staining. ANNA‐2 in 8 of 32 cases bound to podocyte nuclei but not to the 170 kDa protein. Healthy subjects and control neurological and cancer patients lack ANNA‐3. Neurological accompaniments, subacute and usually multifocal, included sensory/sensorimotor neuropathies, cerebellar ataxia, myelopathy, brain stem and limbic encephalopathy. All of 9 adults followed had an intrathoracic neoplasm, seven biopsied within 7 months (five small‐cell lung carcinomas and two adenocarcinomas, one lung, one esophagus) and two imaged, one early, the other 3 years later. Thus, immunohistochemical and Western blot criteria can now identify six IgG markers of neurological autoimmunity related to small‐cell carcinoma, their frequency being ANNA‐1 > collapsin response‐mediator protein‐5 > amphiphysin > Purkinje cell cytoplasmic antibody‐2 = ANNA‐2 = ANNA‐3.

Adiponectin is protective against oxidative stress induced cytotoxicity in amyloid-beta neurotoxicity.

Beta-amyloid (Aβ ) neurotoxicity is important in Alzheimer’s disease (AD) pathogenesis. Aβ neurotoxicity causes oxidative stress, inflammation and mitochondrial damage resulting in neuronal degeneration and death. Oxidative stress, inflammation and mitochondrial failure are also pathophysiological mechanisms of type 2 diabetes (T2DM) which is characterized by insulin resistance. Interestingly, T2DM increases risk to develop AD which is associated with reduced neuronal insulin sensitivity (central insulin resistance). We studied the potential protective effect of adiponectin (an adipokine with insulin-sensitizing, anti-inflammatory and anti-oxidant properties) against Aβ neurotoxicity in human neuroblastoma cells (SH-SY5Y) transfected with the Swedish amyloid precursor protein (Sw-APP) mutant, which overproduced Aβ with abnormal intracellular Aβ accumulation. Cytotoxicity was measured by assay for lactate dehydrogenase (LDH) released upon cell death and lysis. Our results revealed that Sw-APP transfected SH-SY5Y cells expressed both adiponectin receptor 1 and 2, and had increased AMP-activated protein kinase (AMPK) activation and enhanced nuclear factor-kappa B (NF-κB) activation compared to control empty-vector transfected SH-SY5Y cells. Importantly, adiponectin at physiological concentration of 10 µg/ml protected Sw-APP transfected SH-SY5Y cells against cytotoxicity under oxidative stress induced by hydrogen peroxide. This neuroprotective action of adiponectin against Aβ neurotoxicity-induced cytotoxicity under oxidative stress involved 1) AMPK activation mediated via the endosomal adaptor protein APPL1 (adaptor protein with phosphotyrosine binding, pleckstrin homology domains and leucine zipper motif) and possibly 2) suppression of NF-κB activation. This raises the possibility of novel therapies for AD such as adiponectin receptor agonists.

Ischemic Stroke and Intracranial Hemorrhage With Aspirin, Dabigatran, and Warfarin Impact of Quality of Anticoagulation Control

Background and Purpose— Little is known about the impact of quality of anticoagulation control, as reflected by time in therapeutic range (TTR), on the effectiveness and safety of warfarin therapy in Chinese patients with atrial fibrillation. We investigated the risks of ischemic stroke and intracranial hemorrhage (ICH) in relation to warfarin at various TTRs in a real-world cohort of Chinese patients with atrial fibrillation receiving warfarin and compared with those on dabigatran, aspirin, and no therapy. Methods— This is an observational study. Results— Of 8754 Chinese patients with atrial fibrillation and CHA2DS2-VASc ≥1 (79.5±9.2 years; CHA2DS2-VASc, 4.1±1.5; and Hypertension, Abnormal Renal/Liver Function, Stroke, Bleeding History or Predisposition, Labile International Normalized Ratio, Elderly (>65 years), Drugs/Alcohol Concomitantly [HAS-BLED], 2.2±0.9), 16.3% received warfarin, 41.1% aspirin, 4.5% dabigatran, and 38.1% received no therapy. The incidence of ischemic stroke was highest in patients with no therapy (10.38%/y), followed by patients on aspirin (7.95%/y). The incidence of stroke decreased progressively with increasing TTR quartiles (<17.9%, 17.9%–38.8%, 38.8%–56.2%, and >56.2%) from 7.34%/y (first quartile) to 3.10%/y (fourth quartile). Patients on dabigatran had the lowest incidence of stroke among all groups (2.24%/y). The incidence of ICH was lowest in patients on dabigatran (0.32%/y) compared with those on warfarin (0.90%/y), aspirin (0.80%/y), and no therapy (0.53%/y). ICH incidence decreased with increasing TTR from 1.37%/y (first quartile) to 0.74%/y (fourth quartile). Conclusions— In Chinese patients with atrial fibrillation, the benefits of warfarin therapy for stroke prevention and ICH risk are closely dependent on the quality of anticoagulation, as reflected by TTR. Even at the top TTR quartile, warfarin was associated with a higher stroke and ICH risk than dabigatran.

Frequency of seronegativity in adult-acquired generalized myasthenia gravis

We determined the prevalence of muscle acetylcholine receptor (AChR) antibodies in patients with adult‐acquired generalized myasthenia gravis (MG), the seroconversion rate at 12 months, and the prevalence of muscle‐specific tyrosine kinase (MuSK) antibody among persistently seronegative patients. We identified 562 consecutive Mayo Clinic patients with MG based on clinical and electrophysiological criteria. At presentation, 508 patients (90.4%) tested positive for AChR binding or AChR modulating antibodies. After 12 months, 15.2% of initially seronegative patients had become seropositive, yielding a seronegativity rate of 8.2% (95% confidence interval: 6.2–9.6%). Among seronegative patients not receiving immunosuppressants, 38% were MuSK antibody‐positive and 43% were seropositive for nonmuscle autoantibodies. Classification as seronegative MG should be reserved for nonimmunosuppressed patients with generalized MG who lack muscle AChR binding, AChR modulating, or MuSK antibodies at presentation and at follow‐up of at least 12 months. Muscle Nerve, 2007

Mitochondrial neuronal uncoupling proteins: a target for potential disease-modification in Parkinson's disease

This review gives a brief insight into the role of mitochondrial dysfunction and oxidative stress in the converging pathogenic processes involved in Parkinsons disease (PD). Mitochondria provide cellular energy in the form of ATP via oxidative phosphorylation, but as an integral part of this process, superoxides and other reactive oxygen species are also produced. Excessive free radical production contributes to oxidative stress. Cells have evolved to handle such stress via various endogenous anti-oxidant proteins. One such family of proteins is the mitochondrial uncoupling proteins (UCPs), which are anion carriers located in the mitochondrial inner membrane. There are five known homologues (UCP1 to 5), of which UCP4 and 5 are predominantly expressed in neural cells. In a series of previous publications, we have shown how these neuronal UCPs respond to 1-methyl-4-phenylpyridinium (MPP+; toxic metabolite of MPTP) and dopamine-induced toxicity to alleviate neuronal cell death by preserving ATP levels and mitochondrial membrane potential, and reducing oxidative stress. We also showed how their expression can be influenced by nuclear factor kappa-B (NF-κB) signaling pathway specifically in UCP4. Furthermore, we previously reported an interesting link between PD and metabolic processes through the protective effects of leptin (hormone produced by adipocytes) acting via UCP2 against MPP+-induced toxicity. There is increasing evidence that these endogenous neuronal UCPs can play a vital role to protect neurons against various pathogenic stresses including those associated with PD. Their expression, which can be induced, may well be a potential therapeutic target for various drugs to alleviate the harmful effects of pathogenic processes in PD and hence modify the progression of this disease.

Abnormal diffusion tensor in nonsymptomatic familial amyotrophic lateral sclerosis with a causative superoxide dismutase 1 mutation

To determine whether diffusion abnormalities can be observed in nonsymptomatic family members with a known causative Cu/Zn superoxide dismutase mutation (asymptomatic familial amyotrophic lateral sclerosis; AFALS+SOD1) in a family with autosomal dominant familial amyotrophic lateral sclerosis (ALS) using diffusion tensor imaging (DTI).

Human neuronal uncoupling proteins 4 and 5 (UCP4 and UCP5): structural properties, regulation, and physiological role in protection against oxidative stress and mitochondrial dysfunction

Uncoupling proteins (UCPs) belong to a large family of mitochondrial solute carriers 25 (SLC25s) localized at the inner mitochondrial membrane. UCPs transport protons directly from the intermembrane space to the matrix. Of five structural homologues (UCP1 to 5), UCP4 and 5 are principally expressed in the central nervous system (CNS). Neurons derived their energy in the form of ATP that is generated through oxidative phosphorylation carried out by five multiprotein complexes (Complexes I–V) embedded in the inner mitochondrial membrane. In oxidative phosphorylation, the flow of electrons generated by the oxidation of substrates through the electron transport chain to molecular oxygen at Complex IV leads to the transport of protons from the matrix to the intermembrane space by Complex I, III, and IV. This movement of protons to the intermembrane space generates a proton gradient (mitochondrial membrane potential; MMP) across the inner membrane. Complex V (ATP synthase) uses this MMP to drive the conversion of ADP to ATP. Some electrons escape to oxygen‐forming harmful reactive oxygen species (ROS). Proton leakage back to the matrix which bypasses Complex V resulting in a major reduction in ROS formation while having a minimal effect on MMP and hence, ATP synthesis; a process termed “mild uncoupling.” UCPs act to promote this proton leakage as means to prevent excessive build up of MMP and ROS formation. In this review, we discuss the structure and function of mitochondrial UCPs 4 and 5 and factors influencing their expression. Hypotheses concerning the evolution of the two proteins are examined. The protective mechanisms of the two proteins against neurotoxins and their possible role in regulating intracellular calcium movement, particularly with regard to the pathogenesis of Parkinsons disease are discussed.

Mitochondrial UCP4 attenuates MPP+-and dopamine-induced oxidative stress, mitochondrial depolarization, and ATP deficiency in neurons and is interlinked with UCP2 expression

Mitochondrial uncoupling proteins (UCPs) uncouple oxidative phosphorylation from ATP synthesis. We explored the neuroprotective role of UCP4 with its stable overexpression in SH-SY5Y cells, after exposure to either MPP(+) or dopamine to induce ATP deficiency and oxidative stress. Cells overexpressing UCP4 proliferated faster in normal cultures and after exposure to MPP(+) and dopamine. Differentiated UCP4-overexpressing cells survived better when exposed to MPP(+) with decreased LDH release. Contrary to the mild uncoupling hypothesis, UCP4 overexpression resulted in increased absolute ATP levels (with ADP/ATP ratios similar to those of controls under normal conditions and ADP supplementation) associated with increased respiration rate. Under MPP(+) toxicity, UCP4 overexpression preserved ATP levels and mitochondrial membrane potential (MMP) and reduced oxidative stress; the preserved ATP level was not due to increased glycolysis. Under MPP(+) toxicity, the induction of UCP2 expression in vector controls was absent in UCP4-overexpressing cells, suggesting that UCP4 may compensate for UCP2 expression. UCP4 function does not seem to adhere to the mild uncoupling hypothesis in its neuroprotective mechanisms under oxidative stress and ATP deficiency. UCP4 overexpression increases cell survival by inducing oxidative phosphorylation, preserving ATP synthesis and MMP, and reducing oxidative stress.

Mitochondrial UCP5 is neuroprotective by preserving mitochondrial membrane potential, ATP levels, and reducing oxidative stress in MPP+ and dopamine toxicity.

We explored the protective mechanisms of human neuronal mitochondrial uncoupling protein-5 (UCP5) in MPP(+)- and dopamine-induced toxicity after its stable overexpression in SH-SY5Y cells. We raised specific polyclonal antibodies. Overexpressed UCP5 localized in mitochondria but not in cytosol. UCP5 overexpression increased proton leak, decreased mitochondrial membrane potential (MMP), reduced ATP production, and increased overall oxygen consumption (demonstrating uncoupling activity). UCP5 overexpression did not affect other neuronal UCP expression (UCP2 and UCP4). Overexpressing UCP5 is protective against MPP(+)- and dopamine-induced toxicity. MPP(+) and dopamine exposure for 6h reduced MMP and increased superoxide levels. ATP levels in UCP5-overexpressing cells were preserved under MPP(+) and dopamine toxicity, comparable to levels in untreated vector controls. At 24h, UCP5 overexpression preserved MMP, ATP levels, and cell survival; attenuated superoxide generation; and maintained oxidative phosphorylation as indicated by lower lactate levels. MPP(+) and dopamine exposure induced UCP5 mRNA transcription but did not decrease transcript degradation, as inhibition of transcription by actinomycin-D abolished induction by either toxin. Compared with our previous studies on UCP4, we observed functional differences between UCP4 and UCP5 in enhancing mitochondrial efficiency. These neuronal UCP homologues may work synergistically to maintain oxidative balance (through uncoupling activities) and ATP production (by modifying MMP).

Quantitative assessment of the cervical spinal cord damage in neuromyelitis optica using diffusion tensor imaging at 3 Tesla.

To investigate whether quantitative MRI measures of cervical spinal cord white matter (WM) using diffusion tensor imaging (DTI) in neuromyelitis optica (NMO) differed from controls and correlated with clinical disability.