Kathleen M. Rice

Lecithin increases plasma free choline and decreases hepatic steatosis in long-term total parenteral nutrition patients

Plasma-free choline levels have previously been found below normal in patients receiving long term parenteral nutrition (TPN). In a group of 15 patients receiving home TPN who had low plasma free choline levels (6.3 +/- 0.8 mmol/L), we found 50% had hepatic steatosis. These patients were given oral lecithin or placebo in a double-blind randomized trial for 6 weeks. Lecithin supplementation led to an increase in plasma free choline of 53.4% +/- 15.4% at 2 weeks (P = 0.04), which continued at 6 weeks. The placebo group had no change in plasma-free choline at 2 weeks, but a significant decrease of 25.4% +/- 7.1% (P = 0.01) at 6 weeks. A significant and progressive decrease in hepatic fat was indicated by increased liver-spleen CT Hounsfield units at 2 and 6 weeks (7.5 +/- 1.7 units, P = 0.02; 13.8 +/- 3.5 units, P = 0.03) in the lecithin supplemental group. Nonsignificant changes were seen in the placebo group. It was concluded that hepatic steatosis in many patients receiving long term TPN is caused by plasma-free choline deficiency and may be reversed with lecithin supplementation. Choline is a conditionally essential nutrient in this population.

Low plasma free choline is prevalent in patients receiving long term parenteral nutrition and is associated with hepatic aminotransferase abnormalities

Hepatic transaminase abnormalities have been previously reported in patients receiving long term total parenteral nutrition (PN). We sought to determine if such abnormalities are caused by choline deficiency-induced hepatocyte damage. In 41 subjects (19 male, 22 female) aged 45.1 +/- 24.3 years (range 0.1-79 years) who have received PN for 5.5 +/- 4.7 years (range 0.1-14.5 years). We determined plasma free and phospholipid bound choline levels, serum albumin, ALT and AST. We also determined the daily volume of intravenous lipid emulsion received by the patients as well as the concentration of free choline and phospholipid bound choline in the lipid emulsion. Plasma free choline was low in 33 41 subjects (mean 7.15 +/- 2.5 nmol/ml, range 3.3-15.6, normal 11.4 +/- 3.7). Phospholipid bound choline was normal in 34 41 subjects (mean 2157 +/- 620 nmol/ml, range 1026-3887, normal 2364 +/- 774). Elevations in ALT and AST were significantly correlated with plasma free choline (r = -0.34, p = 0.03, r = -0.37, p = 0.02 respectively) but not with phospholipid bound choline. No relationship was found between age, PN duration or daily volume of intravenous lipid and plasma free or phospholipid bound choline. The lipid emulsion contained 24 +/- 6 nmol/ml of free choline and 11 630 +/- 552 nmol/ml of phospholipid bound choline. We conclude that low plasma free choline is prevalent in patients receiving long term PN and this abnormality is associated with elevated serum aminotransferases. Furthermore, intravenous lipid emulsion is an inadequate source of choline for this patient group.

Abnormal erythrocyte choline and influx in Alzheimer's disease

Choline transport and levels were studied in erythrocytes from patients with Alzheimers disease and age-matched controls using stable isotopic tracer techniques. The mean erythrocyte choline in the Alzheimer group was 50.1 nmol ml-1 compared to 15.5 nmol ml-1 in the controls. This was significant using a Students t test at a P of less than 0.0005. Influx of choline into the erythrocyte correlated inversely with erythrocyte choline with high significance. This study suggests that erythrocyte choline is elevated in a subset of patients with Alzheimers disease and that the low affinity transport system is also abnormal in these patients. This abnormality of choline transport may play a role in the pathogenesis of Alzheimers disease in some patients.

Changes in presynaptic release of acetylcholine during development of tolerance to the anticholinesterase, DFP.

Abstract: The rat myenteric plexus was used as a peripheral model for studying muscarinic modulation of acetylcholine (ACh) release from presynaptic muscarinic neurons during development of tolerance to the anticholinesterase agent, diisopropylfluorophosphate (DFP). DFP in arachis oil was administered subcutaneously to intact animals according to both acute and chronic regimens, with arachis oil injections serving as controls. Postmortem analyses showed that the mean AChE activity level in whole brain was reduced under all DFP conditions to 18.0 ± 1.4% when compared with the control level. After 10 days of DFP treatment, the AChE level was 22.3 ± 2.1% of control in the myenteric plexus. There were no significant differences among the treatment groups in resting ACh release. Release evoked by electrical stimulation (difference between stimulated and resting release) in the absence of atropine, i.e., “basal rate,” for strips taken at various times after a single injection of DFP did not differ from that for strips from animals receiving arachis oil only. However, basal release for strips from chronically treated subjects was significantly greater than that of controls (p < 10−3), although not different from each other. Analysis of variance (ANOVA) for repeated measures showed that there existed a highly significant atropine dependency in strips from all treatments when they were stimulated in concentrations of atropine from 10−9 to 10−5M (p < 10−10). Further analyses established that the increases in rates of evoked ACh release as concentrations of atropine increased were similar for strips from chronically treated DFP and arachis oil animals. The overall results show that a significant effect of chronic depression in AChE activity is disinhibition of ACh‐evoked release from presynaptic neurons. This is consistent with the model in which muscarinic autoreceptors control evoked ACh release. The results are also consistent with time parameters for maximum decreases in [3H]quinuclidinyl benzilate binding in brain during chronic DFP treatments such as the regimens used in the present experiments.

Choline pharmacokinetics during intermittent intravenous choline infusion in human subjects

A study of choline pharmacokinetics was undertaken in four patients receiving long‐term total parenteral nutrition. On consecutive days, 7, 14, 28, and 56 mmol choline chloride were intravenously infused over a 12‐hour period in each subject. The choline concentration was determined in plasma at baseline, ¼, 1, 3, 6, and 12 hours, and 3 and 12 hours after the infusion ended, and in daily 24‐hour urine collections. Analysis of variance showed the data fit a two‐compartment model in which elimination from the central compartment was saturable significantly better than a one‐compartment model in all four subjects (p < 10 −8 in all cases), and significantly better than a nonsaturating model in three of the four subjects (p = 1.0 × 10−9, 7.5 × 10−6, 9.4 × 10−11, respectively). The model allowed estimates of the rate constant for choline elimination at ambient levels, first‐order rate constants for transfer between central and peripheral compartments, the dissociation constant for the saturable elimination process, the apparent volume of distribution in the central compartment, the steady‐state volume of distribution, and the quantities of choline in the central compartment and in the readily exchangeable pool.

Global in vivo replacement of choline by N-aminodeanol. Testing a hypothesis about progressive degenerative dementia: I. Dynamics of choline replacement

Severe disruption of certain cholinergic pathways is a characteristic feature of Alzheimers disease. Attempts to establish animal models by interfering with cholinergic function have not been very successful. We now present data which show a substantial and progressive replacement of free and phospholipid-bound choline by the novel choline isostere N-amino-N,N-dimethylaminoethanol during its dietary administration in place of choline. Free choline in blood fell to approximately 20% of controls after 10 to 30 days on diet. Phospholipid-bound choline in plasma was reduced to less than 15%, and in erythrocytes to about 22%. After 120 days of diet free and bound choline were reduced in most tissues to approximately 30% of controls. Only liver retained more than 80% of free choline. Acetylcholine was decreased to 33 to 50% of control. Total true and false transmitter in experimental animals was in all tissues less that acetylcholine in controls, suggesting that muscarinic transmission would be impaired. Moderate reduction of choline acetyltransferase activity was seen in striatum and myenteric plexus, and of QNB-binding in hippocampus, striatum and myenteric plexus.

Roles of neurotransmitter receptors in behavior: recovery of function following decreases in muscarinic receptor density induced by cholinesterase inhibition

Cholinergic neurotransmitter levels were elevated in rat brain by reducing its inactivating enzyme, acetylcholinesterase (AChE), with an anti-AChE agent. Elevated levels result in decreases in cholinergic (muscarinic) receptors. Withdrawal of agent after 10 days of chronic treatment began a gradual return of neurochemical variables toward normal states, yet not fully achieving them within the following 29 days of the experiment. All behavioral and physiological variables measured showed significant effects at the start of the treatment period, developing tolerance at different rates as treatments continued. They also recovered differentially during withdrawal. Results are consistent with a theoretical model in which thresholds for normal functioning of different behavioral and physiological processes are associated with different receptor densities.

Incomplete reversibility of an experimentally induced hypocholinergic state: Biochemical and physiological, but not behavioral, recovery

In previous reports, we described the experimental development of a hypocholinergic state in rats following the total replacement of dietary choline by an artificial isostere, N-aminodeanol (NADe). NADe shares most of the physicochemical and biochemical characteristics of choline (Ch) but is utilized less efficiently in pathways leading to the formation of both acetylcholine and phospholipids. This experimental model mimics many of the features of human degenrative dementias. We now discuss the behavioral and physiological effects of restoring a normal diet after the hypocholinergic state has become well established. The procedure by which that state was induced has been described in detail in earlier publications. After replacing Ch in the diets of weanling rats for 270 days, NADe replaced 70-85% of the phospholipid-bound Ch in plasma, brain, and peripheral tissue. When dietary NADe was removed and Ch was restored in the diet, NADe disappeared and plasma and erythrocyte (RBC) choline levels returned to normal within 30-60 days. Quinuclidinyl benzilate (QNB) binding showed that muscarinic receptors continued to be depressed in animals remaining on the NADe diet, but returned to control levels in the reversal group. There were no differences in cholinesterase activity among the three treatments. Choline acetyltransferase activity returned to control levels, while continuing to be lower in the NADe animals. Liver lipids were elevated in the latter and not significantly different in the control and reversal groups. Among physiological functions, body weight increased more rapidly in the reversal group than in animals continuing on the NADe diet. Brain weights of the reversal animals were significantly greater than those of animals not reversed, but less than controls. Core body temperatures did not differ from controls at any time during the reversal period. Behaviorally, nociceptive thresholds indicative of sensory-reflexive and sensory-perceptual responses remained significantly below normal, that is, a hyperalgesic state. Reversal animals also remained hyperactive and displayed memory significantly poorer than those on the normal diet, that is, no improvement over animals continuing on NADe. In general, the results suggest that behavioral losses induced by NADe reflect persisting changes in the CNS, despite essentially complete recovery of biochemical parameters. The changes may be morphological or be associated with adaptive changes in other neurochemical events in the CNS.

Unexpected Synergism between an Alkylating Analog of Oxotremorine and Soman

We and our colleagues have recently described some potent analogs of oxotremorine containing a /3-chloroethylamine group which cyclize spontaneously in neutral aqueous solution to form reactive aziridinium ions (Ehlert et al., 1984; Ringdahl et al., 1984). These reactive species have a high affinity for the muscarinic receptor, and react with it to form a covalently bound complex. The immediate effects of most of these compounds resemble those of classical muscarinic agonists, but these effects are followed by a prolonged period of resistance to muscarinic agonists which may be due to desensitization, to irreversible receptor occupation, or to both (Gyorgy et al., 1971; Ehlert et al., 1984; Russell et al., 1985). Because of the well-known protective effect of muscarinic antagonists against the cholinergic effects of cholinesterase inhibitors, we studied the interactions of one of these compounds (BM 123: iV-4-(2-chloroethylamino)-2-butynyl-2-pyrollidine) with the organophosphate cholinesterase inhibitor soman. We report here an unexpected synergism between BM 123 and soman and some experiments intended to elucidate its mechanism.