Ursula Kopp

Platelet membrane fluidity individuals at risk for Alzheimer’s disease: a comparison of results from fluorescence spectroscopy and electron spin resonance spectroscopy

Rationale: Previous fluorescence studies employing 1,6-diphenyl-1,3,5-hexatriene (DPH) have revealed an increase in the fluidity of platelet membranes from individuals with Alzheimer’s disease (AD) and their first-degree relatives. This biophysical alteration has been reported to be relatively specific for the hydrocarbon core of platelet membranes, where DPH preferentially localizes; this effect is not reflected by the fluorescent reporter triethylamino-DPH, which labels membranes at the lipid-aqueous interface. Objective: The goal of this study was to explore the validity and reproducibility of these findings using an independent biophysical technique, electron spin resonance (ESR) spectroscopy. Methods: Platelet membranes prepared from first-degree relatives of patients with AD were labeled with DPH, or the spin-labeled fatty acid probes 5-doxylstearate (5-DS) and 12-doxylstearate (12-DS). These spin labeled probes provide an index of structural order at the respective depths of their nitroxide moieties in the membrane. The resulting preparations were examined by fluorescence and ESR spectroscopy. Results: Increased platelet membrane fluidity (PMF), as determined by the fluorescence anisotropy of DPH, was associated with only a modest reduction in the order parameter derived for 5-DS labeled membranes. In contrast, the mean order parameters derived from the paired samples labeled with 12-DS differed substantially from each other, and revealed decreased order (increased fluidity) in the hydrocarbon 12-C region where DPH preferentially localizes. Conclusions: These results provide an independent validation of the biophysical alterations of platelet membranes that are manifested by a subgroup of patients with AD and their first-degree relatives.

Red Blood Cell Abnormalities in Alzheimer Disease

In a prospective, double‐blind study of 84 unselected persons in a dementia clinic, the red blood cell/plasma choline ratios were found to be significantly higher in 47 subjects with clinically defined Alzheimer disease (DAT) than in 37 non‐DAT, nondepressed subjects (3.54 ± 0.48 versus 2.04 ± 0.34, p < 0.02). The latter group included intellectually intact subjects as well as patients with other dementias who were comparable to the Alzheimer patients in age, sex, and degree of cognitive impairment. The elevated mean ratio reflected the greater proportion of Alzheimer patients with high red blood cell plasma choline ratios. These elevated ratios appeared to be related to both increases in red cell content and decreases in plasma choline. The authors conclude that the results confirm and extend those previously reported in short series of patients and agree with other evidence that Alzheimer disease has systemic manifestations in nonneural cells, which may be useful in further investigations of the diseases cellular pathophysiology.

Elevated red blood cell/plasma choline ratio in dimentia of the Alzheimer type: Clinical and polysomnographic correlates

In a prospective study we have observed a shift in distribution of red blood cell (RBC)/plasma choline ratios among patients with probable dementia of the Alzheimer type (DAT), compared with healthy controls and depressed patients. Fifteen of 22 DAT patients (68%) showed RBC/plasma choline ratios greater than 1.9, in contrast to 9 of 26 healthy controls (35%) and 7 of 20 depressives (35%). These significant differences confirm and expand earlier observations. The subgroup of DAT patients with elevated RBC/plasma choline ratios is older and more cognitively impaired, shows later onset of dementia, and has less rapid eye movement (REM) sleep than the DAT subgroup with normal RBC/plasma choline ratios. Within the entire group of DAT patients, moreover, the RBC/plasma choline ratio shows a significant inverse correlation with REM sleep latency. These findings are discussed in relation to abnormalities in other nonneural Alzheimer tissues and within the context of cholinergic involvement in both DAT and the timing of REM sleep.

Blood Choline and its Meaning in Psychiatric and Neurologic Disease States

The involvement of central cholinergic mechanisms has been implicated in a variety of neurologic disease states. These include such syndromes as tardive dyskinesia (11,17,28,32,62), Huntington’s disease (3-5,13,17,18,26,33,49,59,72,84,85,87,90), Friedreich’s ataxia (6,47), presenile dementia of Alzheimer’s type (10,14-16,25,63,64,69,77,89), and Gilles de laTourette’s disease (31,35,66). In all these syndromes a reduction in normal cholinergic activity has been implicated. As a result, attempts have been initiated over the past five years, with variable success, to alleviate some of the associated symptoms, using agents shown in animal experiments to be effective cholinomimetic agents (8). To date, however, use of direct cholinergic agonists and/or antagonists in the treatment of various neurologic, and particularly psychiatric disorders, is still in the experimental phase; such agents have not yet superceded conventionally used psychotherapeutic agents.

Erythrocyte choline transport in drug-free and lithium-treated individuals

The choline (Ch) content of erythrocytes (RBCs) has been reported to be elevated in several psychiatric and neurologic disorders. The present investigation was conducted in order to examine the relationship between in vivo RBC Ch content and Ch flux across the RBC membrane (measured in vitro). To perform the in vitro studies, we measured the outward transport of endogenous Ch (DoCh efflux) and the concomitant inward transport of deuterated Ch (D4Ch influx), in RBCs that were incubated in physiologic media for 24 min at 17 degrees C. Transport of the Ch isotopes was linear during these incubations. In drug-free, psychiatrically normal control subjects, DoCh efflux was inversely correlated with the natural logarithm of in vivo RBC Ch content (r = -0.97, p less than 0.001), and there was a nearly significant correlation between D4Ch influx and in in vivo RBC Ch content (r = -0.81, p less than 0.06). In patients with bipolar affective disorder, lithium treatment both inhibited DoCh and D4Ch transport, and substantially elevated in vivo RBC Ch content. However, varying degrees of transport inhibition were produced by this drug in different subjects. Our findings suggest that membrane Ch transport may have a role in the regulation of endogenous RBC Ch content. Studies of membrane Ch transport in RBCs or other types of cells could potentially help to increase our understanding of cholinergic function in psychiatric or neurologic disorders.

Elevated Red Cell to Plasma Choline Ratios in Alzheimer’s Disease

Alois Alzheimer originally described the disease that bears his name as a form of premature aging and degeneration of the nervous system (1). Since then, most studies have focused on it as a disease of neurones — most recently, of specific populations of large cholinergic neurones in the nucleus basalis and of larger neurons in association cortex (7, 39). In the last five years, however, a number of reports have appeared of abnormalities in non-neural cells from patients with Alzheimer disease (DAT). These include lymphocytes (32, 33, 35), leukocytes (26), cultured skin fibroblasts (2), and red blood cells (3, 13, 15, 23). Four groups have reported that some patients with Alzheimer’s disease have abnormally high levels of choline in their red cells (3, 13, 15, 23). Values were expressed as a ratio of red blood cell to plasma choline, to allow for dietary variation. We now confirm this finding in a prospective, double-blind study of 118 subjects, and discuss the implications of these and other abnormalities in non-neural tissues for the pathophysiology of neuronal cell damage in Alzheimer’s disease.

Blood Cholinergic Parameters as a Potential Index of Central Cholinergic Function

Experiments have been conducted in our laboratories to establish whether it is feasible to utilize red blood cell (RBC) and plasma choline (Ch) as an index of brain cholinergic function in vivo (Shih, T.-M. et al., Neurosci. Abstr. 3, 322, 1977). An animal model has been developed which has provided encouraging results justifying the initiation of parallel studies of RBC and plasma Ch profile in human subjects. Our studies to date in human subjects indicate that: (1) within an individual, RBC and plasma Ch levels are maintained at an unusually constant level for months, provided external conditions and dietary factors are unchanged; (2) tremendous interindividual differences, on the other hand, do exist in RBC Ch levels, and they have been shown to span over a 20-fold range (Hanin, I., et al., Cholinergic Mechanisms and Psychopharmacology, D.J. Jenden, Ed., Plenum, New York, pp. 181–195, 1978); (3) these differences among individuals may furthermore be related in some manner to differences in the behavioral state of these individuals. Unipolar depressed, drug-free patients were shown to have significantly higher RBC Ch levels (51.7 ± 18.4 nmol/ml;n= 1 5) than normal controls (10.2 ± 1.0 nmol/ml; n = 10). Plasma Ch levels, at the same time, were similar in both groups; (4) finally, treatment of depressed patients with the antidepressant, amitriptyline (Elavil®), had no effect on RBC and plasma Ch levels, implying that endogenous factors play a major role in controlling the levels of RBC and plasma Ch in various individuals. We believe that the higher observed levels of RBC Ch in some of our depressed patients are related in some very specific manner to the concept of a definitive involvement of cholinergic mechanisms in affective disease states. The nature and extent of this relationship are currently under further investigation in our laboratories. Supported by NIMH grant No. MH 26320.