Cross-linked Aggregates Research Articles

Cross-Linked Amorphous Nitrilase Aggregates for Enantioselective Nitrile Hydrolysis

A recombinant Escherichia coli strain was constructed which efficiently expressed the enantioselective nitrilase from Alcaligenes faecalis DSMZ 30030 as a hisitidine-tagged enzyme variant under the control of a rhamnose inducible promoter. The enzyme was purified from cell extracts and used for the preparation of cross-linked enzyme aggregates (CLEAs). The conditions for the preparation of the CLEAs were optimized using various organic solvents and cross-linking agents and a procedure was developed which combined a precipitation with 85 % (v/v) isopropyl alcohol and a cross-linking with 30 mM glutaraldehyde. Thus, about 80 % of the initial nitrilase activity could be incorporated into the CLEAs. The hydrolysis of racemic mandelonitrile to (R)-mandelic acid was compared between the soluble nitrilase preparations and their CLEAs (nit-CLEAs). The nitrilase activity in the CLEAs was at 30 °C and 60 °C about 5 times more stable than in the soluble preparations. The CLEAs could be reused 5 times with only about 10 % reduction in activity. The enantioselectivity of the nitrilase for the formation of (R)-mandelic acid from racemic mandelonitrile decreased for both preparations with increasing temperatures (10 °C to 50 °C), but this effect was significantly less pronounced for the CLEAs. A detailed analysis of solvent effects on nitrilase enantioselectivity allowed thermodynamic insights into contributions from free energy component (activation enthalpy and entropy) to chiral preference of nitrilase in such non conventional media.

Preparation and characterization of cross-linked laccase aggregates and their application to the elimination of endocrine disrupting chemicals

Laccase from the white rot fungus Coriolopsis polyzona was immobilized for the first time through the formation of cross-linked enzyme aggregates (CLEAs). Laccase CLEAs were produced by using 1000 g of polyethylene glycol per liter of enzyme solution as precipitant and 200 μM of glutaraldehyde as a cross-linking agent. These CLEAs had a laccase activity of 148 U g −1 and an activity recovery of 60.2% when using 2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) as substrate. CLEAs formed by co-aggregation with bovine serum albumin (BSA) as a stabilizer showed lower laccase activity and affinity for ABTS than those without BSA. The CLEAs co-aggregated with BSA showed higher residual activity against a protease, NaN 3, EDTA, methanol and acetone. The thermoresistance was higher for CLEAs than for free laccase and also higher for CLEAs co-aggregated with BSA than for simple CLEAs when tested at a pH of 3 and a temperature of 40 °C. Finally, laccase CLEAs were tested for their capacity to eliminate the known or suspected endocrine disrupting chemicals (EDCs) nonylphenol, bisphenol A and triclosan in a fluidized bed reactor. A 100-ml reactor with 0.5 mg of laccase CLEAs operated continuously at a hydraulic retention time of 150 min at room temperature and pH 5 could remove all three EDCs from a 5 mg l −1 solution.

Asymmetric synthesis of cyanohydrin derived from pyridine aldehyde with cross-linked aggregates of hydroxynitrile lyases

Enantiocomplementary R- and S-cyanohydrins with >93% ee were synthesized through the hydrocyanation of 3-pyridinecarboxaldehyde in >65% yield. Hydroxynitrile lyases (HNLs) from cassava and almond were used in commercially available cross-linked enzyme aggregate (CLEA) forms to catalyze the reactions and produce material with optical purities significantly greater than has been reported previously. The use of a dichloromethane reaction system with enzyme aggregates and free hydrogen cyanide was crucial in improving cyanohydrin stereoselectivity through minimizing background racemic cyanide addition and enzyme-catalyzed racemization of the product.

Retraction of “Preferential degradation of oxidized proteins by the 20S proteasome may be inhibited in aging and in inflammatory neuromuscular diseases”

Free radicals produced by chronic inflammation cause cumulative damage to cellular macromolecules and appear to contribute to senescence/aging, age-related disorders, and neuromuscular degenerative diseases such as inclusion-body myositis. Proteins are major targets for oxidative damage (in addition to DNA and lipids) and the accumulation of oxidized proteins has been reported in many aging and disease models. In young and healthy individuals, moderately oxidized soluble cell proteins are selectively and rapidly degraded by the 20S proteasome. The mechanism of selective proteolysis appears to depend upon oxidation-induced protein unfolding, with increasing surface hydrophobicity as (previously shielded) hydrophobic residues are exposed from the interior. The 20S proteasome can preferentially bind to and degrade such mildly oxidized, hydrophobic proteins without a need for ubiquitin targeting or ATP activation. Severely oxidized, aggregated, and crosslinked proteins, however, are poor substrates for degradation and actually inhibit the proteasome. During aging, and in many age-related diseases/disorders, the proteasome is progressively inhibited by binding to increasing levels of oxidized and cross-linked protein aggregates. Cellular aging and inflammatory neuromuscular degenerative diseases probably include both an increase in the generation of reactive oxygen species as well as a decline in proteasome activity, resulting in the progressive accumulation of oxidatively damaged protein aggregates that eventually contribute to cellular dysfunction and senescence.

A new method for spectrophotometric assay of activity of cross-linked penicillin acylase aggregates

A new method for monitoring reactions catalyzed by an immobilized enzyme, cross-linked penicillin acylase aggregates (PA CLEA), is suggested. Appropriate chromogenic substrates for spectrophotometric assay of catalytic activity of immobilized enzyme were chosen and their kinetic parameters determined. Active sites in PA CLEA preparations were titrated by the suggested method; it is shown that almost all active sites are retained during immobilization. This method is characterized as highly expressive, simple, and precise and may be used for control of PA immobilization efficiency as well as for study of operational, thermal, and pH stability of immobilized enzyme preparations.

The presence of phosphorylation form of D1 protein in its cross-linked aggregates in high light treated spinach leaves in vivo

In the present study, using specific antibody against D1 protein, we detected four aggregates of D1 protein in thylakoid membranes from spinach leaves illuminated at high light (800–2500 μmol photons·m−2·s−1) for 3 h. Their accumulations were dependent on the light intensity to which the leaves had been subjected. Further immunoblot analysis indicated that 70 kD aggregate was a product of D1 protein cross-linked with CP43, 65 and 60 kD aggregate were two cross-linked products between D1 and D2 proteins, and 41 kD aggregate was one cross-linked D1 with α-subunit of cytochrome b559 (Cyt b559). This result provided the evidence for the existence of the aggregation of the D1 protein in vivo. The maximal level of D1/Cyt b559 aggregate occurred at 1000 μmol photons·m−2·s−1 but drastically decreased with further increasing light intensity. Immunoblot analysis with phosphothreonine (Thr (P)) antibody indicated that D1/CP43 and D1/Cyt b559 aggregates contained the phosphorylated protein(s). In vitro dephosphorylation experiment also showed that D1/Cyt b559 and D1/CP43 aggregates lost the immunoreactivity with Thr (P) antibody after the phosphatase treatment of the membranes from high-light-illuminated leaves. Our results demonstrated that strong illumination of spinach leaves induced cross-linked products of D1 protein with its nearby polypeptides of PS, some of which co.n-tained the phosphorylated D1 protein.

Preferential degradation of oxidized proteins by the 20S proteasome may be inhibited in aging and in inflammatory neuromuscular diseases

Free radicals produced by chronic inflammation cause cumulative damage to cellular macromolecules and appear to contribute to senescence/aging, age-related disorders, and neuromuscular degenerative diseases such as inclusion-body myositis. Proteins are major targets for oxidative damage (in addition to DNA and lipids) and the accumulation of oxidized proteins has been reported in many aging and disease models. In young and healthy individuals, moderately oxidized soluble cell proteins are selectively and rapidly degraded by the 20S proteasome. The mechanism of selective proteolysis appears to depend upon oxidation-induced protein unfolding, with increasing surface hydrophobicity as (previously shielded) hydrophobic residues are exposed from the interior. The 20S proteasome can preferentially bind to and degrade such mildly oxidized, hydrophobic proteins without a need for ubiquitin targeting or ATP activation. Severely oxidized, aggregated, and crosslinked proteins, however, are poor substrates for degradation and actually inhibit the proteasome. During aging, and in many age-related diseases/disorders, the proteasome is progressively inhibited by binding to increasing levels of oxidized and cross-linked protein aggregates. Cellular aging and inflammatory neuromuscular degenerative diseases probably include both an increase in the generation of reactive oxygen species as well as a decline in proteasome activity, resulting in the progressive accumulation of oxidatively damaged protein aggregates that eventually contribute to cellular dysfunction and senescence.

Protein oxidation and degradation during postmitotic senescence

Oxidized and cross-linked proteinacious materials (lipofuscin, age pigments, ceroid, etc.) have long been known to accumulate in aging and in age-related diseases, and some studies have suggested that age-dependent inhibition of the proteasome and/or lysosomal proteases may contribute to this phenomenon. Cell culture studies trying to model these aging effects have almost all been performed with proliferating (divisionally competent) cell lines. There is little information on nondividing (postmitotic) cells; yet age-related accumulation of oxidized and cross-linked protein aggregates is most marked in postmitotic tissues such as brain, heart, and skeletal muscles. The present investigation was undertaken to test whether oxidized and cross-linked proteins generally accumulate in nondividing, IMR-90 and MRC-5, human cell lines, and whether such accumulation is associated with diminished proteolytic capacities. Since both protein oxidation and declining proteolytic activities might play major roles in the age-associated accumulation of intracellular oxidized materials, we tested for protein carbonyl formation, proteasomal activities, and lysosomal cathepsin activities. For these studies, confluent, postmitotic IMR-90 and MRC-5 fibroblasts (at various population doubling levels) were cultured under hyperoxic conditions to facilitate age-related oxidative senescence. Our results reveal marked decreases in the activity of both the proteasomal system and the lysosomal proteases during senescence of nondividing fibroblasts, but the peptidyl–glutamyl-hydrolyzing activity of the proteasome was particularly inhibited. This decline in proteolytic capacity was accompanied by an increased accumulation of oxidized proteins.

High‐pressure studies of aggregation of recombinant human interleukin‐1 receptor antagonist: Thermodynamics, kinetics, and application to accelerated formulation studies

Recombinant human interleukin-1 receptor antagonist (IL-1ra) in aqueous solutions unfolds and aggregates when subjected to hydrostatic pressures greater than about 180 MPa. This study examined the mechanism and thermodynamics of pressure-induced unfolding and aggregation of IL-1ra. The activation free energy for growth of aggregates (DeltaG-/+(aggregation)) was found to be 37 +/- 3 kJ/mol, whereas the activation volume (DeltaV-/+(aggregation)) was -120 +/- 20 mL/mol. These values compare closely with equilibrium values for denaturation: The free energy for denaturation, DeltaG(denaturation), was 20 +/- 5 kJ/mol, whereas the partial specific volume change for denaturation, DeltaV(denaturation), was -110 +/- 30 mL/mol. When IL-1ra begins to denature at pressures near 140 MPa, cysteines that are normally buried in the native state become exposed. Under oxidizing conditions, this results in the formation of covalently cross-linked aggregates containing nonnative, intermolecular disulfide bonds. The apparent activation free energy for nucleation of aggregates, DeltaG-/+(nuc), was 42 +/- 4 kJ/mol, and the activation volume for nucleation, DeltaV-/+(nuc),was -175 +/- 37 mL/mol, suggesting that a highly solvent-exposed conformation is needed for nucleation. We hypothesize that the large specific volume of IL-1ra, 0.752 +/- 0.004 mL/g, coupled with its relatively low conformational stability, leads to its susceptibility to denaturation at relatively low pressures. The positive partial specific adiabatic compressibility of IL-1ra, 4.5 +/- 0.7 +/- 10(-12) cm2/dyn, suggests that a significant component of the DeltaV(denaturation) is attributable to the elimination of solvent-free cavities. Lastly, we propose that hydrostatic pressure is a useful variable to conduct accelerated formulation studies of therapeutic proteins.

Co-aggregation of Enzymes and Polyethyleneimine: A Simple Method To Prepare Stable and Immobilized Derivatives of Glutaryl Acylase

We have developed a novel methodology that allowed the preparation of cross-linked enzyme aggregates (CLEAs) of glutaryl acylase (GAC) by co-aggregation of the enzyme with an aminated polymer: polyethyleneimine (PEI). The preparation of CLEAs of GAC from Pseudomonas sp. is not possible when using poly(ethylene glycol) and glutaraldehyde directly as precipitating and cross-linking agent, respectively. This problem arises probably from the low content of surface Lys groups of GAC which prevents an efficient cross-linking of the enzyme molecules in the aggregate. This fact was proven by the release of enzyme molecules from the aggregate and the solubilization of the enzyme when eliminating the precipitating agent. Our new co-aggregation system favors the cross-linking between the very reactive and abundant primary amino groups of the PEI and the primary amino groups on the enzyme surface. The use of PEI prevents the release of enzyme molecules from the aggregate. By this methodology, we prepared a very stable immobilized derivative of GAC. After optimization of the glutaraldehyde treatment conditions, the stability of the enzyme was significantly improved. It kept more than 60% of its initial activity after 72 h of incubation at 45 degrees C, whereas the soluble enzyme was fully inactivated in 2.5 h of incubation in the same conditions. Therefore, we have a new protocol for carrying out the preparation of cross-linked aggregates of enzymes with a low number of lysines on its surface.

Mapping and Analysis of the Lytic and Fusogenic Domains of Surfactant Protein B

Surfactant protein B (SP-B) is a hydrophobic, 79 amino acid peptide that regulates the structure and function of surfactant phospholipid membranes in the airspaces of the lung. Addition of SP-B to liposomes composed of DPPC/PG (7:3) leads to membrane binding, destabilization, and fusion, ultimately resulting in rearrangement of membrane structure. The goal of this study was to map the fusogenic and lytic domains of SP-B and assess the effects of altered fusion and lysis on surface activity. Synthetic peptides were generated to predicted helices and/or interhelical loops of SP-B and tested for fusion, lytic, and surface activities. The N-terminal half of SP-B (residues 1-37), which includes the nonhelical N-terminal amino acids in addition to helices 1 and 2, promoted rapid liposome fusion whereas shorter peptides were significantly less effective. The requirements for optimal surface tension reduction were similar to those for fusion; in contrast, helix 1 (residues 7-22) alone was sufficient for liposome lysis. The C-terminal half of SP-B (residues 43-79), which includes helices 3, 4, and 5, exhibited significantly lower levels of fusogenic, lytic, and surface tension reducing activities compared to the N-terminal region. These results indicate that SP-B fusion, lytic and surface activities map predominantly to the N-terminal half of SP-B. Amino acid substitutions in synthetic peptides corresponding to the N-terminal half of SP-B indicated that, in general, decreased fusion or lytic activities were associated with altered surface tension reducing properties of the peptide. However, the presence of fusion and lytic activities alone could not account for the surface tension reducing property of SP-B. We propose a model in which association of helix 1 with lipids leads to membrane permeabilization but not aggregation; helix 2 mediates membrane cross-linking (aggregation), which, in turn, facilitates lipid mixing, membrane fusion, and interfacial adsorption/surface tension reduction.

Cross-Linked Aggregates of (R)-Oxynitrilase: A Stable, Recyclable Biocatalyst for Enantioselective Hydrocyanation

[Reaction: see text] The (R)-oxynitrilase from almonds was immobilized as a cross-linked enzyme aggregate (CLEA) via precipitation with 1,2-dimethoxyethane and subsequent cross-linking using glutaraldehyde. The resulting preparation was a highly effective hydrocyanation catalyst under microaqueous conditions, which suppress the nonenzymatic background reaction. The beneficial effect of these latter conditions on the hydrocyanation of slow-reacting aldehydes is demonstrated. The oxynitrilase CLEA was recycled 10 times without loss of activity.

Effects of the hydration process on water-soluble proteins of preserved cod products

Electrophoresis and chromatography were used to analyse the water-soluble proteins of fresh, salted and dried cod ( Gadus morhua L.) and of re-hydrated products. Sodium dodecyl sulphate pore gradient gel electrophoresis showed that there was a great loss of water-soluble proteins during stockfish re-hydration. Furthermore, comparison of the electrophoresis patterns of cod products, under reducing and non-reducing conditions, showed the presence of cross-linked protein aggregates, related to the oxidation of SH groups and oxidative stress. Similar results were obtained by high performance liquid chromatography, which confirmed a great loss of water-soluble proteins and a higher level of SH oxidation in hydrated stockfish samples. Finally, capillary electrophoresis allowed definition of the unfolded state of denatured proteins in salted cod. This technique also proved a fast and useful way to differentiate the two products by analysis of water-soluble proteins.

Peroxynitrite reaction with eye lens proteins: alpha-crystallin retains its activity despite modification.

. Peroxynitrite is a highly potent reactive oxygen/nitrogen species present in the environment and also endogenously in the eye, that causes a variety of disorders. This study was undertaken to look at the oxidative damage that peroxynitrite causes to the proteins of the lens and the functional consequences thereof. . Peroxynitrite was allowed to react with alpha-, beta-, and gamma-crystallins. The formation of nitrotyrosine and nitrotryptophan, dityrosine, protein covalent cross-links, and chain degradation products were monitored by spectroscopy and SDS-PAGE. Conformational changes occurring in the protein were monitored with circular dichroism spectroscopy. The chaperoning ability of alpha-crystallin was assayed by monitoring its ability to inhibit the self-aggregation of two test proteins: beta-crystallin and insulin. . Peroxynitrite reaction produced nitrotyrosine, nitrotryptophan, and dityrosine, nondisulfide covalent cross-linked aggregates, and peptide chain degradation. The hydroxyl radicals produced by peroxynitrite caused more chain degradation than did the carbonate radicals. The oxidative reaction caused increased conformational disorder. The yield was highest in gamma-crystallin and least in alpha-crystallin. The chaperoning ability of alpha-crystallin was not affected. . Peroxynitrite reacts with lens proteins, causing extensive covalent chemical changes. However, alpha-crystallin retains its chaperoning ability, despite the oxidative changes caused by the peroxynitrite reaction, indicating its functional robustness.

Immobilization of cross-linked lipase aggregates within microporous polymeric membranes

A new approach is proposed to immobilize lipase into microporous polymeric membrane via embedding cross-linked enzyme aggregates (CLEA) within membrane pores. Preparation of biocatalytic membranes was implemented with hydrophilic cellulose and hydrophobic PTFE membranes. Formation of lipase CLEAs is initiated by solvent exchange between aqueous solution of the enzyme filling membrane pores and organic media containing cross-linking agent. The influence of organic media composition and matrix hydrophilicity/hydrophobicity on membrane biocatalytic properties has been studied. Highly effective biocatalytic membranes with embedded lipase CLEA have been obtained on the base of both hydrophilic and hydrophobic membranes by varying the content of glutaric dialdehyde used as a cross-linking agent. Bio-imprinting has been tested as a mean to improve efficiency of the biocatalytic membranes. Biocatalytic esterification of oleic acid with n-butanol has been studied in cross-flow membrane bioreactor with membrane-supported lipase CLEA using hexane and iso-octane as reaction solvents of different hydrophobicity.

Cross-linking of ubiquitin, HSP27, parkin, and alpha-synuclein by gamma-glutamyl-epsilon-lysine bonds in Alzheimer's neurofibrillary tangles.

The accumulation of misfolded proteins in intracellular inclusions is a generic feature of neurodegenerative disorders. Although heavily ubiquitylated, the aggregated proteins are not degraded by the proteasomes. A possible reason for this phenomenon may be a modification of deposited proteins by transglutaminases forming gamma-glutamyl-epsilon-lysine (GGEL) cross-links between distinct proteins. Here, we show that the frequency of GGEL cross-links is an order of magnitude higher in Alzheimer's brain cortex than in age-matched or younger controls. This difference is due to the accumulation of GGEL cross-links in ubiquitin-immunopositive protein particles present in both Alzheimer's brains and those from aged individuals. The highly cross-linked protein aggregates show immunoreactivity to antibodies against tau and neurofilament proteins, and partially also to alpha-synuclein, indicating that these structures are inherent in Alzheimer's neurofibrillary tangles and Lewy bodies. Using mass sequence analysis, we identified the same six pairs of peptide sequences cross-linked in both senile and Alzheimer's specimens: Gln31 and Gln190 of HSP27 protein are cross-linked with Lys29 and Lys48 of ubiquitin and HSP27 therefore may cross-link two (poly)ubiquitin chains. One lysine residue of parkin and one of alpha-synuclein were also found to be cross-linked. The data suggest that cross-linking of (poly)ubiquitin moieties via HSP27 may have a role in the stabilization of the intraneuronal protein aggregates by interference with the proteasomal elimination of unfolded proteins.

Cross-linked aggregates of multimeric enzymes: a simple and efficient methodology to stabilize their quaternary structure.

In this manuscript, we show that the immobilization of proteins following the technique of cross-linked protein aggregates (CLEAS) may permit the stabilization of the most complex multimeric enzymes by preventing their dissociation. To illustrate that, we have first prepared CLEAS with two tetrameric catalases. Activity recovery was over 40%, and no protein subunit could be desorbed from the CLEAS after boiling in SDS. More interestingly, the enzyme stability, which in its soluble form strongly depends on the enzyme concentration, becomes fully independent of this parameter. This permitted the enzyme stability to greatly increase under diluted conditions. In fact, diluted CLEAs presented a higher stability than those of their glyoxyl derivatives counterparts, which were unable to fully stabilize the multimeric structure of these tetrameric enzymes

X-ray crystal structure of a galactose-specific C-type lectin possessing a novel decameric quaternary structure.

Rattlesnake venom lectin (RSL) from the western diamondback rattlesnake (Crotalus atrox) is an oligomeric galactose-specific C-type lectin. The X-ray crystal structure of RSL, in complex with lactose and thiodigalactoside, at 2.2 and 2.3 A resolution, respectively, reveals a decameric protein composed of two 5-fold symmetric pentamers arranged in a staggered, back-to-back orientation. Each monomer corresponds to a single canonical C-type lectin carbohydrate recognition domain devoid of accessory domains and is disulfide-bonded to a monomer in the other pentamer. The structure is the first example of that of a carbohydrate complex of a vertebrate galactose-specific C-type lectin. The 10 carbohydrate-binding sites, located on the rim of the decamer, suggest a role for multivalent interactions and a mechanism for RSL's ability to promote receptor cross-linking and cell aggregation.

Optimization of Enzymatic Synthesis of Ampicillin Using Cross-Linked Aggregates of Penicillin G Acylase

Penicillin G acylase from E. coli TA1 was immobilized by Cross-Linked Enzyme Aggregates (CLEA), a new method for immobilization. This biocatalyst and commercial immobilized penicillin G acylase (PGA-450) were used to study the effect of pH, temperature and substrate concentration on the synthesis of ampicillin from phenyl glycine methyl ester (PGME) and 6-aminopenicillanic acid (6-APA). Compared with PGA-450, this immobilized enzyme showed a high synthesis activity. The optimum conditions for synthetic activity was at pH 6, 25°C and 2:6 (6-APA:PGME) substrate ratio.

Anti-AGEing defences against Alzheimer's disease.

Accumulation of insoluble protein deposits and their cross-linking by AGEs (advanced glycation end products) in the brain is a feature of aging and neurodegeneration, especially in AD (Alzheimer's disease). In AD, two types of fibrillar protein aggregates are present: extracellular deposits (plaques) consisting mainly of Abeta (beta-amyloid peptide), and intracellular deposits (tangles) composed predominantly of microtubule-associated protein tau. Both plaques and tangles are modified by AGEs, which occurs particularly at lysine and arginine residues. Interaction of a synthetic amyloid plaque (fibrillar Abeta) with microglia leads to a strong pro-inflammatory response, indicating that priming of immune cells with beta-amyloid potentiates their response to secondary stimuli such as AGE and cytokines such as interferon-gamma. Formation of hyperphosphorylated and cross-linked microtubule-associated protein tau aggregates, especially tau dimers as the first step in tangle formation, can be induced in vitro by the combination of okadaic acid, a PP2A phosphatase inhibitor, and methylglyoxal. These results suggest that excess production of reactive carbonyl compound ("carbonyl stress") and subsequent AGE formation can contribute to cross-linking of protein fibrils and to pathological pro-inflammatory signalling, which all contribute to pathological changes and dementia progression in AD. However, the human brain has developed the glyoxalase system, a most effective defence system to scavenge small dicarbonyl compounds such as glyoxal and methylglyoxal. Very importantly, this system needs GSH as a rate-limiting cofactor. Since GSH is limited under conditions of oxidative stress and inflammation, supplementation with antioxidants such as lipoic acid, vitamin E or flavonoids could indirectly strengthen the anti-glycation defence system in AD. In addition, synthetic carbonyl scavengers and anti-inflammatory drugs could also be valuable drugs for the "anti-glycation" treatment of AD.