Impact of Differential Rates of Disease Progression in Amyloid-Positive Early Alzheimer's Disease: Findings from a Longitudinal Cohort Analysis.

BACKGROUND: There is limited literature regarding the impact of differential rates of disease progression on longitudinal outcomes in individuals with early Alzheimer's disease (AD) and confirmed brain amyloid pathology. OBJECTIVES: To describe the underlying characteristics and long-term outcomes associated with different rates of disease progression among amyloid-positive individuals with early symptomatic AD. DESIGN: Retrospective observational study. SETTING: Data from the National Alzheimer's Coordinating Center (NACC) Uniform Data Set (UDS) in the United States (06/2005-11/2021). PARTICIPANTS: Individuals with a clinical assessment of mild cognitive impairment or dementia and Clinical Dementia Rating® Dementia Staging Instrument Sum of Boxes (CDR-SB) score 0.5-9.0 (inclusive; first visit defined as the index date) and confirmed amyloid positivity. Participants were stratified into No Progression (change ≤0), Slower Progression (0< change <2.0 points), Median Progression (2.0-point change), and Faster Progression (change >2.0 points) cohorts based on the observed distribution of changes in CDR-SB score between the index and first subsequent visit. MEASUREMENTS: For each cohort, the functional and neuropsychiatric outcomes were described at index and each subsequent visit for up to five years, and least-square (LS) mean changes from baseline were estimated using linear mixed-effects models adjusting for baseline demographic and clinical characteristics. RESULTS: Among 1,263 participants included in the analysis, the mean±standard deviation (SD) age at index was 72.7±9.7 years and 55.3% were males. Demographic characteristics and comorbidity profiles at index were similar across cohorts. However, at index, the Faster Progression (N=279) cohort had higher CDR-SB and Functional Assessment Questionnaire (FAQ) scores compared with the No Progression (N=474), Slower Progression (N=297), and Median Progression (N=213) cohorts. Adjusting for baseline characteristics, at year 5 after index the FAQ score increased by 23.6 points for Faster Progression cohort and 10.4, 15.8, and 19.2 points for the No, Slower, and Median Progression cohorts, respectively. The corresponding increases in Neuropsychiatric Inventory Questionnaire (NPI-Q) scores were 6.7 points for the Faster Progression cohort, and by 1.3, 3.1, and 8.3 points, for the No, Slower, and Median Progression cohorts, respectively. CONCLUSIONS: Despite similar demographic and clinical profiles at baseline, amyloid-positive individuals with greater deterioration based on CDR-SB early in the AD trajectory continue to experience worse functional and behavioral outcomes over time than those with more gradual deterioration in this metric.

Potential Implications of Slowing Disease Progression in Amyloid-Positive Early Alzheimer's Disease: Estimates from Real-World Data.

BACKGROUND: Emerging therapies have shown promising results for slowing the progression of Alzheimer's disease (AD). However, the potential impact of these therapies on real-world outcomes remains to be explored. OBJECTIVE: To examine the impact of slowing AD progression on functional abilities and behavioral symptoms. DESIGN: Retrospective observational study. SETTING: Data from the National Alzheimer's Coordinating Center (NACC) Uniform Data Set (UDS) in the United States (06/2005-11/2021, primary analysis) and the Alzheimer's Disease Neuroimaging Initiative (ADNI) database (09/2005-03/2022, sensitivity analysis) were used. PARTICIPANTS: Individuals with mild cognitive impairment (MCI) or mild dementia, Clinical Dementia Rating Scale Sum of Boxes (CDR-SB) score 0.5-9.0 (inclusive; first visit defined as the index date), and confirmed amyloid positivity were identified in NACC. In ADNI, individuals with at least one clinical center visit with a clinical assessment of MCI or mild dementia and confirmed amyloid positivity were identified. MEASUREMENTS: Hypothetical effects of slowing disease progression as assessed by CDR-SB on functional and behavioral outcomes including the Functional Activities Questionnaire (FAQ) score, Neuropsychiatric Inventory Questionnaire (NPI-Q) score, and the probability of complete dependence over five years were evaluated using multivariable regression among NACC participants, separately for the subgroups with MCI and mild dementia at baseline, respectively. For the ADNI sensitivity analysis, the hypothetical effects of slowing disease progression were evaluated for FAQ score using multivariable regression among the MCI participants only. RESULTS: Compared with natural disease progression, slowing progression by 20% over five years for NACC participants with MCI and mild dementia, respectively, would result in 1.7-point (10.8%) and 1.6-point (12.9%) less deterioration based on FAQ; 0.5-point (20.3%) and 0.5-point (19.3%) less deterioration based on NPI-Q; 4.7 percentage-point (22.2%) and 10.1 percentage-point (21.6%) lower probability of complete dependence. Among ADNI participants, delaying disease progression by 20% or 30% over 4 years would avert deterioration based on FAQ of 1.1 points (20.4%) and 1.6 points (29.6%), respectively, compared to natural disease progression. CONCLUSIONS: Slowing early AD progression could result in preservation of functional and behavioral attributes and functional autonomy for longer.

T-type Ca2+ channels and alpha1E expression in spermatogenic cells, and their possible relevance to the sperm acrosome reaction.

There is pharmacological evidence that Ca2+ channels play an essential role in triggering the mammalian sperm acrosome reaction, an exocytotic process required for sperm to fertilize the egg. Spermatozoa are small terminally differentiated cells that are difficult to study by conventional electrophysiological techniques. To identify the members of the voltage-dependent Ca2+ channel family possibly present in sperm, we have looked for the expression of the alpha 1A, alpha 1B, alpha 1C, alpha 1D and alpha 1E genes in mouse testis and in purified spermatogenic cell populations with RT-PCR. Our results indicate that all 5 genes are expressed in mouse testis, and in contrast only alpha 1E, and to a minor extent alpha 1A, are expressed in spermatogenic cells. In agreement with these findings, only T-type Ca2+ channels sensitive to the dihydropyridine nifedipine were observed in patch-clamp recordings of pachytene spermatocytes. These results suggest that low-threshold Ca2+ channels are the dihydropyridine-sensitive channels involved in the sperm acrosome reaction.

Structural and functional comparison of toxins from the venom of the scorpions Centruroides infamatus infamatus, Centruroides limpidus limpidus and Centruroides noxius.

Two novel toxins containing 66 amino acid residues each were isolated from the venom of the scorpions Centruroides infamatus infamatus and Centruroides limpidus limpidus, respectively. Their full amino acid sequences were determined. Comparison of primary structures showed that they share 97% similarity among themselves and 83% to that of toxin 2 from Centruroides noxius. The three toxins studied compete with each other for the same binding sites on membranes prepared from rat brain synaptosomes, suggesting that they are all beta-scorpion toxins. Toxin action was assayed into the microI-2 rat skeletal muscle Na+ channel heterologously expressed into Xenopus oocytes. All three toxins block this Na+ channel in a similar fashion, without affecting inactivation, and showed IC50 values in the micromolar concentration range.

Delta-endotoxins induce cation channels in Spodoptera frugiperda brush border membranes in suspension and in planar lipid bilayers.

Membrane potential measurements using a fluorescent dye indicated that two specific toxins active against Spodoptera frugiperda larvae (CryIC and CryID) cause immediate permeability changes in midgut epithelial brush border membrane vesicles (BBMV). The initial response and the sustained permeability change are cationic, not very K+ selective, and occur at in vivo lethal doses (nM). The toxin response has a different ion selectivity and is more sensitive to Ba2+ than the intrinsic cation permeability of BBMV. Experiments incorporating BBMV into planar lipid bilayers (PLB) demonstrated that these vesicles contain cation channels (31, 47 and 76 pS). A 2-40 fold conductance increase was induced by nM concentrations of toxin in PLB containing BBMV. Cationic single channel transitions of 50, 106, 360 and 752 pS were resolved. Thus, Bacillus thuringiensis delta-endotoxins induce an increase in cation membrane permeability involving ion channels in BBMV-containing functional receptors.

Calcium channels in excitable cells: divergent genotypic and phenotypic expression of alpha 1-subunits.

The Ba2+ currents and mRNA levels of four members of the rat brain family of alpha 1-subunit Ca2+ channel genes were examined and compared in the rat cell lines GH3 and PC-12 and in the mouse lines NIE-115 and AtT-20. The RNA was measured with ribonuclease protection assays using probes derived from rat brain (rb) Ca2+ channel cDNAs (rbA, rbB, rbC, and rbD), and the Ba2+ currents were studied by whole cell patch-clamp recording. L-, N-, P-, and T-type currents were discriminated by the voltage dependence and pharmacological properties of Ba2+ currents. All cell lines expressed all four rat brain Ca2+ channel genes, except GH3 cells, which lacked rbB. The functional diversity of Ba2+ currents, however, was quite different among the cell lines. GH3 cells showed evidence of L- and T-type currents, undifferentiated PC-12 cells of L-type currents, AtT-20 cells of L-, N-, and P-type currents, and undifferentiated NIE-115 cells of a T-type current that was partially blocked by both nifedipine and BAY K 8644. Dimethyl sulfoxide-differentiated NIE-115 cells also had an L-type current. Differentiation of NIE-115 cells caused an increase in the levels of rbB, rbC, and rbD RNAs. Differentiation by nerve growth factor caused an increase in levels of all four genes in PC-12. Our data give further support for the assignment of rbA, rbB, and rbC/rbD gene products as components of P-, N-, and L-type Ca2+ channels, respectively.

A high-conductance voltage-dependent multistate Ca2+ channel found in sea urchin and mouse spermatozoa.

Ion fluxes through poorly understood channel-mediated mechanisms participate in the interaction between spermatozoa and egg. Previously, we reported the characterization in planar bilayers of a high conductance Ca(2+)-selective, voltage-dependent multistate channel from S. purpuratus sea urchin sperm plasma membranes. Here we show that this ion channel can be directly transferred to planar lipid bilayers upon sperm addition, from sea urchin (S. purpuratus and L. pictus) and from mouse. We found that spermatozoa from these species possess a conspicuous Ca(2+)-selective, high conductance, multi-state, voltage-dependent channel, which displays similar voltage dependence and equal PBa2+/PK+ approximately 4 in the three species. The presence of this Ca2+ channel in such diverse species suggests it plays a relevant role in sperm physiology. The high sensitivity of planar bilayers to detect single ion channels can now be used to study ion channel regulation and gamete interaction.

Ionic bases of the membrane potential and intracellular pH changes induced by speract in swollen sea urchin sperm.

Signal transduction initiated by the egg peptide, speract, in sea urchin sperm is not fully understood. Hypotonically swollen sperm are a suitable model to study peptide signal transduction. Ion substitution experiments now indicate (i) that the permeability to Na+, Ca2+, and Mg2+ contributes to the sperm resting membrane potential; (ii) the repolarization induced by nM concentrations of speract is Na+ dependent and mediated by an as yet unidentified channel; (iii) the depolarization triggered by nM concentrations of speract involves Ca2+ channels since it is Ca(2+)-dependent and blocked by Co2+ and Ni2+, two Ca2+ channel blockers; (iv) hyperpolarizing swollen sperm with valinomycin increases intracellular pH (pHi) in the same way as speract, thus the speract-induced hyperpolarization may be responsible for the pHi increase.

Ca2+ channels from the sea urchin sperm plasma membrane.

Ca2+ influx across the sea urchin sperm plasma membrane is a necessary step during the egg jelly-induced acrosome reaction. There is pharmacological evidence for the involvement of Ca2+ channels in this influx, but their presence has not been directly demonstrated because of the small size of this cell. Sea urchin sperm Ca2+ channels are being studied by fusing isolated plasma membranes into planar lipid bilayers. With this strategy, a Ca2+ channel has been detected with the following characteristics: (a) the channel exhibits a high mainstate conductance (gamma MS) of 172 pS in 50 mM CaCl2 solutions with voltage-dependent decaying to smaller conductance states at negative Em; (b) the channel is blocked by millimolar concentrations of Cd2+, Co2+, and La3+, which also inhibit the egg jelly-induced acrosome reaction; (c) the gamma MS conductance sequence for the tested divalent cations is the following: Ba2+ greater than Sr2+ greater than Ca2+; and (d) the channel discriminates poorly for divalent over monovalent cations (PCa/PNa = 5.9). The sperm Ca2+ channel gamma MS rectifies in symmetrical 10 mM CaCl2, having a maximal slope conductance value of 94 pS at +100 mV applied to the cis side of the bilayer. Under these conditions, a different single-channel activity of lesser conductance became apparent above the gamma MS current at positive membrane potentials. Also in 10 mM Ca2+ solutions, Mg2+ permeates through the main channel when added to the cis side with a PCa/PMg = 2.9, while it blocks when added to the trans side. In 50 mM Ca2+ solutions, the gamma MS open probability has values of 1.0 at voltages more positive than -40 mV and decreases at more negatives potentials, following a Boltzmann function with an E0.5 = -72 mV and an apparent gating charge value of 3.9. These results describe a novel Ca2(+)-selective channel, and suggest that the main channel works as a single multipore assembly.

Incorporation of ionic channels from yeast plasma membranes into black lipid membranes.

Recently, patch-clamping of yeast protoplasts has revealed the presence of plasma membrane K+ channels (Gustin, M. C., B. Martinac, Y. Saimi, M. R. Culberston, and C. Kung. 1986. Science (Wash. DC). 233:1195-1197). In this work we show that fusion of purified plasma membranes into planar bilayers allows the study of the yeast channels. The main cationic conductances detected were of 64 and 116 pS, however, larger and smaller conductances have been observed. The two main conductances were sensitive to the K+ channels blockers tetraethylammonium (TEA+) and Ba2+. Bionic experiments indicated that both conductances were K+ selective.

Purification and reconstitution of potassium channel proteins from squid axon membranes.

Voltage-dependent K+ channels are responsible for repolarization of the cell membrane during the late phase of the action potential. Here we report the purification of proteins from squid axon membranes which bind the K+-channel blocker noxiustoxin (NTX), and their subsequent functional reconstitution in planar bilayers. The NTX-affinity purified proteins had Mr values of 60,000 +/- 6,000, 160,000 +/- 15,000 and 220,000 +/- 20,000. Their incorporation into bilayers resulted in single-channel currents with three conductances, the most frequent one of 11 pS in 300/100 mM KCl (cis/trans). The voltage dependence, reversal potential and bursting behavior suggest that these are the K+ channels involved in the squid axon action potential.

Single-channel activity of bilayers derived from sea urchin sperm plasma membranes at the tip of a patch-clamp electrode.

Changes in the plasma membrane permeability of echinoderm sperm play a fundamental role in the acrosome reaction. During the reaction there is an increase in intracellular Ca2+ and Na+ and an efflux of H+ and K+. We have formed bilayers at the tip of patch pipets from a mixture of lipid vesicles and sea urchin sperm plasma membranes (12-50 microgram protein/ml). We observed three types of K+ channels (conductances: 22, 46, and 82 pS), two of which are partially blocked by TEA, and one Cl- channel (148 pS). The presence of K+ channels in sperm plasma membranes is consistent with the inhibition by TEA of the acrosome reaction in whole sperm and the membrane potential change that occurs during the reaction.