Modulation of proteasome activity by curcumin and didemethylcurcumin

Modulation of proteasome function by pharmacological interventions and molecular biology tools is an active area of research in cancer biology and neurodegenerative diseases. Curcumin (diferuloylmethane) is a naturally occurring polyphenol that affects multiple signaling pathways. Curcumin shows anti-inflammatory, antioxidant, anti-angiogenic, or anti-apoptotic properties. Recent research suggests that the therapeutic efficacy of curcumin may be due to its activity as a potent inhibitor of the proteasome. Using in vitro cell culture and molecular docking methods, here we show that both curcumin and its synthetic polyphenolic derivative (didemethylcurcumin, CUIII) modulated proteasome activity in a biphasic manner. Curcumin and CUIII increased proteasome activity at nanomolar concentrations, but inhibited proteasome activity at micromolar concentrations. Curcumin was more effective than CUIII in increasing relative proteasome activity at nanomolar concentrations. Also, curcumin was more effective than CUIII in inhibiting relative proteasome activity at micromolar concentrations. Docking simulations of curcumin and didemethylcurcumin binding to the 20S proteasome catalytic subunit estimated Kd values of 0.0054 µM and 1.3167 µM, respectively. These values correlate well with the results of the effectiveness of modulation by curcumin compared to CUIII. The small size of CUIII allows it to dock to the narrow cavity of the active site, but the binding interaction is not strong compared to curcumin. These results indicate that curcumin and its didemethyl derivative can be used to modulate proteasome activity and suggest that curcumin and its didemethyl derivative may be useful in treating two different disease classes: neurodegeneration and cancer.Communicated by Ramaswamy H. Sarma.

An Algorithm for Preclinical Diagnosis of Alzheimer's Disease

Almost all Alzheimer's disease (AD) therapeutic trials have failed in recent years. One of the main reasons for failure is due to designing the disease-modifying clinical trials at the advanced stage of the disease when irreversible brain damage has already occurred. Diagnosis of the preclinical stage of AD and therapeutic intervention at this phase, with a perfect target, are key points to slowing the progression of the disease. Various AD biomarkers hold enormous promise for identifying individuals with preclinical AD and predicting the development of AD dementia in the future, but no single AD biomarker has the capability to distinguish the AD preclinical stage. A combination of complimentary AD biomarkers in cerebrospinal fluid (Aβ₄₂, tau, and phosphor-tau), non-invasive neuroimaging, and genetic evidence of AD can detect preclinical AD in the in-vivo ante mortem brain. Neuroimaging studies have examined region-specific cerebral blood flow (CBF) and microstructural changes in the preclinical AD brain. Functional MRI (fMRI), diffusion tensor imaging (DTI) MRI, arterial spin labeling (ASL) MRI, and advanced PET have potential application in preclinical AD diagnosis. A well-validated simple framework for diagnosis of preclinical AD is urgently needed. This article proposes a comprehensive preclinical AD diagnostic algorithm based on neuroimaging, CSF biomarkers, and genetic markers.

Bryostatin and its synthetic analog, picolog rescue dermal fibroblasts from prolonged stress and contribute to survival and rejuvenation of human skin equivalents

Skin health is associated with the day-to-day activity of fibroblasts. The primary function of fibroblasts is to synthesize structural proteins, such as collagen, extracellular matrix proteins, and other proteins that support the structural integrity of the skin and are associated with younger, firmer, and more elastic skin that is better able to resist and recover from injury. At sub-nanomolar concentrations (0.03-0.3 nM), bryostatin-1 and its synthetic analog, picolog (0.1-10 nM) sustained the survival and activation of human dermal fibroblasts cultured under the stressful condition of prolonged serum deprivation. Bryostatin-1 treatment stabilized human skin equivalents (HSEs), a bioengineered combination of primary human skin cells (keratinocytes and dermal fibroblasts) on an extracellular matrix composed of mainly collagen. Fibroblasts activated by bryostatin-1 protected the structural integrity of HSEs. Bryostatin-1 and picolog prolonged activation of Erk in fibroblasts to promote cell survival. Chronic stress promotes the progression of apoptosis. Dermal fibroblasts constitutively express all components of Fas associated apoptosis, including caspase-8, an initiator enzyme of apoptosis. Prolong bryostatin-1 treatment reduced apoptosis by decreasing caspase-8 and protected dermal fibroblasts. Our data suggest that bryostatin-1 and picolog could be useful in anti-aging skincare, and could have applications in tissue engineering and regenerative medicine.

Alzheimer's Disease Cerebrospinal Fluid and Neuroimaging Biomarkers: Diagnostic Accuracy and Relationship to Drug Efficacy

Widely researched Alzheimer's disease (AD) biomarkers include in vivo brain imaging with PET and MRI, imaging of amyloid plaques, and biochemical assays of Aβ 1 - 42, total tau, and phosphorylated tau (p-tau-181) in cerebrospinal fluid (CSF). In this review, we critically evaluate these biomarkers and discuss their clinical utility for the differential diagnosis of AD. Current AD biomarker tests are either highly invasive (requiring CSF collection) or expensive and labor-intensive (neuroimaging), making them unsuitable for use in the primary care, clinical office-based setting, or to assess drug efficacy in clinical trials. In addition, CSF and neuroimaging biomarkers continue to face challenges in achieving required sensitivity and specificity and minimizing center-to-center variability (for CSF-Aβ 1 - 42 biomarkers CV = 26.5% ; http://www.alzforum.org/news/conference-coverage/paris-standardization-hurdle-spinal-fluid-imaging-markers). Although potentially useful for selecting patient populations for inclusion in AD clinical trials, the utility of CSF biomarkers and neuroimaging techniques as surrogate endpoints of drug efficacy needs to be validated. Recent trials of β- and γ-secretase inhibitors and Aβ immunization-based therapies in AD showed no significant cognitive improvements, despite changes in CSF and neuroimaging biomarkers. As we learn more about the dysfunctional cellular and molecular signaling processes that occur in AD, and how these processes are manifested in tissues outside of the brain, new peripheral biomarkers may also be validated as non-invasive tests to diagnose preclinical and clinical AD.

Peripheral biomarkers of Alzheimer's disease

Currently available diagnostic tests have moved the field closer to early diagnosis of Alzheimer's disease (AD); however, a definitive diagnosis is made only with the development of clinical dementia and the presence of amyloid plaques and neurofibrillary tangles at autopsy. An ideal antemortem AD biomarker should satisfy the following criteria: the ability to diagnose AD with high sensitivity and specificity as confirmed by the gold standard of autopsy validation; the ability to detect early-stage disease and track the progression of AD; and monitor therapeutic efficacy. AD biomarker technologies currently under development include in vivo brain imaging with PET and MRI (i.e., imaging of amyloid plaques, biochemical assays in cerebrospinal fluid (CSF) and peripheral tissues. CSF biomarkers have received increased attention in the past decade. However, it is unclear whether these biomarkers are capable of early diagnosis of AD, prior to Aβ accumulation, or whether they can differentiate between AD and non-AD dementias. In addition, CSF biomarkers may not lend themselves to diagnostic screening of elderly patients, given the invasiveness of lumbar puncture, inter-laboratory variability in techniques and sample handling, and the circadian fluctuation of CSF components. Although commonly viewed as an abnormality of the brain, AD is a systemic disease with associated dysfunction in metabolic, oxidative, inflammatory, and biochemical pathways in peripheral tissues, such as the skin and blood cells. This has led researchers to investigate and develop assays of peripheral AD biomarkers (a few with high sensitivity and specificity) that require minimally invasive skin or blood samples.

PKCε deficits in Alzheimer's disease brains and skin fibroblasts

In Alzheimer's disease (AD) transgenic mice, activation of synaptogenic protein kinase C ε (PKCε) was found to prevent synaptotoxic amyloid-β (Aβ)-oligomer elevation, PKCε deficits, early synaptic loss, cognitive deficits, and amyloid plaque formation. In humans, to study the role of PKCε in the pathophysiology of AD and to evaluate its possible use as an early AD-biomarker, we examined PKCε and Aβ in the brains of autopsy-confirmed AD patients (n = 20) and age-matched controls (AC, n = 19), and in skin fibroblast samples from AD (n = 14), non-AD dementia patients (n = 14), and AC (n = 22). Intraneuronal Aβ levels were measured immunohistochemically (using an Aβ-specific antibody) in hippocampal pyramidal cells of human autopsy brains. PKCε was significantly lower in the hippocampus and temporal pole areas of AD brains, whereas Aβ levels were significantly higher. The ratio of PKCε to Aβ in individual CA1 pyramidal cells was markedly lower in the autopsy AD brains versus controls. PKCε was inversely correlated with Aβ levels in controls, whereas in AD patients, PKCε showed no significant correlation with Aβ. In autopsy brains, PKCε decreased as the Braak score increased. Skin fibroblast samples from AD patients also demonstrated a deficit in PKCε compared to controls and an AD-specific change in the Aβ-oligomer effects on PKCε. Together, these data demonstrate that the relationship between Aβ levels and PKCε is markedly altered in AD patients' brains and skin fibroblasts, reflecting a loss of protective effect of PKCε against toxic Aβ accumulation. These changes of PKCε levels in human skin fibroblasts may provide an accurate, non-invasive peripheral AD biomarker.

Spatiotemporal complexity of fibroblast networks screens for Alzheimer's disease

Drugs to treat Alzheimer's disease (AD) have been unsuccessful in preventing its devastating cognitive deficits and progressive neurodegeneration. The lack of a definitive diagnostic for AD has been a major obstacle to AD drug discovery. Here, we describe a novel, highly accurate peripheral diagnostic for AD patients based on quantitatively measured complexity of skin-sampled fibroblast networks. A significant number of samples were studied under double-blind conditions and had autopsy and/or genetic validation. An additional sample confirmed the diagnostic discrimination on freshly obtained skin samples. A sub-sample of these diagnostic differences were induced by oligomerized amyloid-β1-42. Based on the accuracy of these measures that utilize physical principles such as fractal dimension and lacunarity as well as the significant correlation with disease duration, this biomarker profile appears to identify accurately AD patients for therapeutic intervention.

A cellular model of Alzheimer's disease therapeutic efficacy: PKC activation reverses Abeta-induced biomarker abnormality on cultured fibroblasts

PKC signaling is critical for the non-toxic degradation of amyloid precursor protein (APP) and inhibition of GSK3beta, which controls phosphorylation of tau protein in Alzheimer's disease (AD). Thus the misregulation of PKC signaling could contribute to the origins of AD. Bryostatin, a potent PKC modulator, has the potential to ameliorate both the neurodegeneration and the recent memory loss associated with AD. As reported herein bryostatin and a potent synthetic analog (picolog) are found to cause stimulation of non-amyloidogenic pathways by increasing alpha-secretase activity and thus lowering the amount of toxic Abeta produced. Both bryostatin and picolog increased the secretion of the alpha-secretase product (s-APP-alpha) of APP at sub-nanomolar to nanomolar concentrations. A peripheral AD-Biomarker has previously been autopsy-validated. This Biomarker, based on bradykinin-induced differential phosphorylation of Erk1 and Erk2, has been used here to test the therapeutic efficacy both for bryostatin and picolog. Both of these PKC activators are then shown to convert the AD Erk1/2 phenotype of fibroblasts into the phenotype of "normal" control skin fibroblasts. This conversion occurred for both the abnormal Erk1/2 phenotype induced by application of Abeta(1-42) to the fibroblasts or the phenotype observed for fibroblasts of AD patients. The Abeta(1-42)-induction, and PKC modulator reversal of the AD Erk1/2 biomarker phenotype demonstrate the AD-Biomarker's potential to monitor both disease progression and treatment response. Additionally, this first demonstration of the therapeutic potential in AD of a synthetically accessible bryostatin analog warrants further preclinical advancement.

An internally controlled peripheral biomarker for Alzheimer's disease: Erk1 and Erk2 responses to the inflammatory signal bradykinin

Cognitive impairment has recently been found to correlate with changes in peripheral inflammatory signals such as TNF-alpha and IL-1beta. PKC isozymes regulate levels of TNF-alpha and IL-6 and the release of other cytokines and also show deficits in Alzheimer's disease (AD) brains and skin fibroblasts. Here, we investigate MAPK Erk1 and Erk2 phosphorylation in response to the inflammatory agonist bradykinin, which activates PKC pathways. An internally controlled comparison of Erk1 and Erk2 produced an AD index that accurately distinguished fibroblasts of AD from those of normal controls and of non-AD dementias. This accuracy was demonstrated for Coriell Cell Repository (Coriell Institute of Medical Research, Camden, NJ) samples, as well as for samples analyzed on gels with autopsy diagnostic confirmation. AD Erk1 and Erk2 index values were inversely correlated with disease duration, suggesting maximal efficacy for early diagnosis. Finally, the results also demonstrate that, when the AD index agreed with the clinical diagnosis on the presence of AD, there was a high probability of accuracy based on autopsy validation. Thus, this peripheral molecular biomarker, based on differential Erk1 and Erk2 phosphorylation, could have important clinical utility for providing increased certainty in the positive diagnosis of AD, particularly in the early phase of disease progression.

Calcium-induced aggregation of archaeal bipolar tetraether liposomes derived from the thermoacidophilic archaeon Sulfolobus acidocaldarius

Previously, we showed that the proton permeability of small unilamellar vesicles (SUVs) composed of polar lipid fraction E (PLFE) from the thermoacidophilic archaeon Sulfolobus acidocaldarius was remarkably low and insensitive to temperature (Komatsu and Chong 1998). In this study, we used photon correlation spectroscopy to investigate the time dependence of PLFE SUV size as a function of Ca2+ concentration. In the absence of Ca2+, vesicle diameter changed little over 6 months. Addition of Ca2+, however, immediately induced formation of vesicle aggregates with an irregular shape, as revealed by confocal fluorescence microscopy. Aggregation was reversible upon addition of EDTA; however, the reversibility varied with temperature as well as incubation time with Ca2+. Freeze-fracture electron microscopy showed that, after a long period of incubation (2 weeks) with Ca2+, the PLFE vesicles had not just aggregated, but had fused or coalesced. The initial rate of vesicle aggregation varied sigmoidally with Ca2+ concentration. At pH 6.6, the threshold calcium concentration (Cr) for vesicle aggregation at 25 and 40 degrees C was 11 and 17 mM, respectively. At pH 3.0, the Cr at 25 degrees C increased to 25 mM. The temperature dependence of Cr may be attributable to changes in membrane surface potential, which was -22.0 and -13.2 mV at 25 and 40 degrees C, respectively, at pH 6.6, as determined by 2-(p-toluidinyl)naphthalene-6-sulfonic acid fluorescence. The variation in surface potential with temperature is discussed in terms of changes in lipid conformation and membrane organization.

Binding of NAP-22, a calmodulin-binding neuronal protein, to raft-like domains in model membranes

The cholesterol-binding protein NAP-22 is a major component of the detergent-insoluble low-density fraction of rat brain. In this study, we found, using fluorescence microscopy, that native NAP-22, but not a demyristoylated form, binds to cholesterol-rich raft-like domains in planar-supported monolayers and remains bound after nonionic detergent extraction. NAP-22 also protects the cholesterol-rich domains during extraction by methyl-beta-cyclodextrin. The lateral mobility of this protein is much lower than that of other raft components in model membranes, suggesting that both cholesterol binding and inter-NAP-22 interactions markedly reduce its lateral diffusion. This study suggests that NAP-22 binding may be employed to image cholesterol-rich regions, such as caveolae/rafts, on the plasma membrane of cells, and preliminary efforts in that direction are presented.

Two-photon fluorescence microscopy studies of bipolar tetraether giant liposomes from thermoacidophilic archaebacteria Sulfolobus acidocaldarius

The effects of temperature and pH on Laurdan (6-lauroyl-2-(dimethylamino)naphthalene) fluorescence intensity images of giant unilamellar vesicles (GUVs) ( approximately 20-150 microm in diameter) composed of the polar lipid fraction E (PLFE) from the thermoacidophilic archaebacteria Sulfolobus acidocaldarius have been studied using two-photon excitation. PLFE GUVs made by the electroformation method were stable and well suited for microscopy studies. The generalized polarization (GP) of Laurdan fluorescence in the center cross section of the vesicles has been determined as a function of temperature at pH 7.23 and pH 2.68. At all of the temperatures and pHs examined, the GP values are low (below or close to 0), and the GP histograms show a broad distribution width (> 0.3). When excited with light polarized in the y direction, Laurdan fluorescence in the center cross section of the PLFE GUVs exhibits a photoselection effect showing much higher intensities in the x direction of the vesicles, a result opposite that previously obtained on monopolar diester phospholipids. This result indicates that the chromophore of Laurdan in PLFE GUVs is aligned parallel to the membrane surface. The x direction photoselection effect and the low GP values lead us to further propose that the Laurdan chromophore resides in the polar headgroup region of the PLFE liposomes, while the lauroyl tail inserts into the hydrocarbon core of the membrane. This unusual L-shaped disposition is presumably caused by the unique lipid structures and by the rigid and tight membrane packing in PLFE liposomes. The GP exhibited, at both pH values, a small but abrupt decrease near 50 degrees C, suggesting a conformational change in the polar headgroups of PLFE. This transition temperature fully agrees with the d-spacing data recently measured by small-angle x-ray diffraction and with the pyrene-labeled phosphatidylcholine and perylene fluorescence data previously obtained from PLFE multilamellar vesicles. Interestingly, the two-photon Laurdan fluorescence images showed snowflake-like lipid domains in PLFE GUVs at pH 7.23 and low temperatures (<20 degrees C in the cooling scan and <24 degrees C in the heating scan). These domains, attributable to lipid lateral separation, were stable and laterally immobile at low temperatures (<23 degrees C), again suggesting tight membrane packing in the PLFE GUVs.

Studies of archaebacterial bipolar tetraether liposomes by perylene fluorescence

Membrane packing and dynamics of bipolar tetraether liposomes composed of the polar lipid fraction E (PLFE) from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius have been studied by perylene fluorescence. At a probe-to-PLFE lipid ratio of 1:400, we have detected an unusual fluorescence intensity increase with increasing temperature, while the fluorescence lifetime changed little. As the ratio was decreased, the intensity anomaly was diminished. At 1:3200 and 1:6400, the anomaly disappeared. A remarkable perylene intensity anomaly was also observed in bilayers composed of saturated monopolar diester phosphatidylcholines at their main phase transition temperatures. These results suggest that the intensity anomaly may be due to probe aggregation caused by tight membrane packing. At the same probe-to-lipid ratio (1:400), however, 1, 2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and 1, 2-diphytanoyl-sn-glycero-3-phosphoglycerol (DPhPG) liposomes did not exhibit any intensity anomaly with increasing temperature. This suggests that DPhPC and DPhPG liposomes are more loosely packed than PLFE liposomes; thus the branched methyl groups are not the contributing factor of the tight membrane packing found in PLFE liposomes. Using a multiexcitation method, we have also determined the average (R), in-plane (R(ip)), and out-of-plane (R(op)) rotational rates of perylene in PLFE liposomes at various temperatures (20-65 degrees C). R and R(ip), determined at two different probe-to-lipid ratios (1:400 and 1:3200), both undergo an abrupt increase when the temperature is elevated to approximately 48 degrees C. These data suggest that PLFE liposomes are rigid and tightly packed at low temperatures, but they begin to possess appreciable "membrane fluidity" at temperatures close to the minimum growth temperature ( approximately 50 degrees C) of thermoacidophilic archaebacteria.