Mats Lindström

Aqueous lipid phases of relevance to intestinal fat digestion and absorption.

The phase behavior of monoglyceride/water systems, with oleic and linoleic acid as the dominating fatty acid residues, was investigated. Increased solubilization of triglycerides (oil) or oleic acid in the cubic liquid-crystalline phase formed by monoglyceride and water resulted in the formation of a reversed hexagonal liquid-crystalline phase followed by an L2-phase. The liquid-crystalline phases have different dispersion properties compared to each other in dilute micellar bile salt solutions. The cubic phase is found to be easily dispersed. The relevance of aqueous lipid phases other thah micellar is discussed in relation to intestinal lipid digestion and absorption.

Impulsivity related to brain serotonin transporter binding capacity in suicide attempters.

Altered monoaminergic activity has earlier been associated with violent suicidal behaviour. In this study whole brain binding potential of the serotonin transporter (5HTT) and dopamine transporter (DAT) was measured by single photon emission computerised tomography (SPECT) in 12 patients after a serious suicide attempt and in 12 age, sex and season matched healthy controls. Clinical and temperamental assessments were analysed for possible associations with 5HTT and DAT. We found no significant 5HTT or DAT differences between patients and controls. In patients, but not in controls, there was a significant correlation between whole brain 5HTT and DAT. Impulsiveness according to the Marke Nyman Temperament (MNT) was significantly correlated to 5HTT in suicide attempters, but not in controls. Neither of the transporters could be regarded as a marker for serious suicidal behaviour. A previously discussed connection between serotonin and dopamine was replicated in this study. In suicide attempters, low 5HTT was associated with impulsivity and to some extent with depressive disorder-key factors for suicidal behaviour.

Concerted action of human carboxyl ester lipase and pancreatic lipase during lipid digestion in vitro: importance of the physicochemical state of the substrate

The pancreatic enzyme carboxyl ester lipase (CEL) has been shown to hydrolyse a large number of different esters, including triacylglycerols, cholesteryl esters and retinyl esters with an absolute requirement for bile salts. Some of the lipids that are substrates for CEL can also be hydrolysed by pancreatic lipase. In order to investigate the relative roles of human CEL and pancreatic lipase, the two enzymes were incubated on a pH-stat with isotope-labelled lipid substrate mixtures in physicochemical forms resembling the state of the dietary lipids in human intestinal contents. In the first set of experiments, cholesteryl oleate (CO) and retinyl palmitate (RP) were solubilised in an emulsion of triolein (TO) stabilised by egg phosphatidylcholine and bile salts. Lipase (always added together with its cofactor, colipase) hydrolysed TO, with monoolein and oleic acid as end-products, whereas CEL alone could not hydrolyse TO in the presence of phosphatidylcholine (PC). Lipase alone did not hydrolyse CO or RP, but CEL did hydrolyse these esters if lipase was present. Release of [3H]glycerol from labelled TO increased only slightly if CEL was added compared to lipase alone, suggesting that monoolein hydrolysis was slow under these conditions. In the second set of experiments, CO and RP were dissolved in bile salt/monoolein/oleic acid dispersions with varying bile salt concentrations. CEL hydrolysed CO and RP more rapidly in a system with a high bile salt concentration containing mixed micelles than in a system with a low bile salt concentration, where the lipids were dispersed in the form of mixed micellar and non-micellar aggregates; both types of aggregate have been reported to exist in human intestinal contents. In conclusion, these data suggest that the main function of CEL under physiological conditions is to hydrolyse cholesteryl and retinyl esters, provided that the triacylglycerol oil phase is hydrolysed by pancreatic lipase, which probably causes a transfer of the substrate lipids of CEL from the oil emulsion phase to an aqueous bile salt/lipolytic product phase. Depending on the bile salt/lipolytic product ratio, the substrate will reside in either micellar or non-micellar lipid aggregates, of which the micellar state is preferred by CEL.

Regional brain serotonin and dopamine transporter binding capacity in suicide attempters relate to impulsiveness and mental energy.

To study different aspects of regional pre-synaptic brain (123)I-beta-CIT uptake on serotonin and dopamine re-uptake sites in drug-free suicide attempters in comparison with age- and sex matched control subjects, single photon emission computed tomography (SPECT) measurements were analysed for regional serotonin re-uptake (5HTT) and dopamine re-uptake (DAT) capacity (binding potential, BP()) after i.v. (123)I-beta-CIT administration. All suicide attempters were examined concerning seriousness of the attempt, and DSM-IV diagnosis. Both suicide attempters and control subjects were tested for psychotropic drugs, and completed the Marke-Nyman Temperament (MNT) test, including solidity (level of impulsiveness/initiative) and validity (level of mental energy). We found no significant difference between suicide attempters and control subjects concerning the regional levels of 5HTT BP() or DAT BP(). However, in suicide attempters, but not controls, we found significant regional correlations between MNT variables and SPECT results. We interpret the discrepant findings in suicide attempters and control subjects to be due to a disability of the suicide attempters to regulate their serotonin and dopamine levels, e.g. in response to external stress.

Serotonin transporter gene polymorphisms: Effect on serotonin transporter availability in the brain of suicide attempters

The efficacy of serotonin reuptake inhibitors in depression and anxiety disorders suggests the gene coding for the serotonin transporter (5-HTT), SLC6A4, as a candidate of importance for these conditions. Positive findings regarding associations between polymorphisms in SLC6A4 have been reported, indicating that these polymorphisms may influence anxiety-related personality traits, as well as the risk of developing depression and suicidality. Serotonin 5-HTT availability was assessed with single photon emission computed tomography (SPECT), using (123)I-beta-CIT as ligand, in a population of unmedicated male suicide attempters (n=9) and in matched controls (n=9). Two polymorphisms in SLC6A4 were assessed, including the 5-HTTLPR located in the promoter region and a variable number of tandem repeats (VNTR) polymorphism in intron 2 (STin2). In suicide attempters, but not in controls, low 5-HTT availability was associated with the S allele of 5-HTTLPR and with the 12 repeat allele of STin2. Data suggest that polymorphisms in SLC6A4 may influence the expression of the brain serotonin transporter in suicide attempters.

Genetic Variation in Brain-Derived Neurotrophic Factor Is Associated with Serotonin Transporter but Not Serotonin-1A Receptor Availability in Men

BACKGROUND The serotonergic system, including the serotonin transporter (5-HTT), which is the target of many antidepressants, seems to be influenced by brain-derived neurotrophic factor (BDNF). METHODS Positron emission tomography (PET) was used to address, in 25 and 53 healthy volunteers, respectively, the possible association between six polymorphisms in the gene encoding BDNF and the availability of two proteins expressed by serotonergic neurons: the 5-HTT, measured with the radioligand [(11)C]MADAM, and the serotonin-1A (5-HT1A) receptor, measured with [(11)C]WAY-100635. RESULTS Several single nucleotide polymorphisms were associated with [(11)C]MADAM binding potential (BP) in most brain regions, male carriers of the valine/valine genotype of the Val66Met polymorphism displaying higher availability. Effect sizes ranged from a 50% to a threefold increase. In contrast, there was no association for [(11)C]WAY-100635 BP. The observation that BDNF polymorphisms were associated with 5-HTT availability could be partly replicated in an independent population comprising nine male suicide attempters and nine matched control subjects, in which transporter availability had been measured with single photon emission computed tomography with (123)I-beta-CIT as ligand. CONCLUSIONS Our results suggest that genetic variation in BDNF influences 5-HTT but not 5-HT1A receptor density in the human brain.

Size of basal ganglia in suicide attempters, and its association with temperament and serotonin transporter density.

Magnetic resonance imaging was used to compare subcortical volumes of seven suicide attempters with those of six healthy controls. Suicide attempters had 10% smaller right caudate nucleus and 19% bilaterally smaller globus pallidus. In suicide attempters, volumes of the globus pallidus correlated negatively with previously reported measures of solidity (non-impulsive temperament) and serotonin transporter binding potential.

Calcium binding to porcine pancreatic prophospholipase A2 studied by 43Ca NMR

Pancreatic phospholipase Aa (PLA,) catalyzes the hydrolysis of fatty acid ester bonds at the 2-position of 1,2-diacyl sn-phospholipids [ 11. The enzyme is secreted by the pancreas in an inactive form. In the duodenum the zymogen is activated by trypsin cleavage [ 11. The enzyme is capable of degrading phospholipids in micellar form, while the proenzyme is only able to hydrolyze monomeric substrates [2,3]. It has been shown that Ca” are essential for the catalytic properties of both the enzyme and the zymogen. Ca” binding to both forms has been studied by a variety of physicochemical techniques, showing that Ca’+ binds in a 1: 1 molar ratio with association constants in the range of l-5 X lo3 M-’ [4,5]. From X,ray crystallographic data the Ca” binding site has been found to be located in a cavity of the protein surface near Aspd9 [ 61. Here we report the results of 43Ca NMR measurements of Ca2+ binding to prophospholipase A, (PPLA,). It is shown that the method is useful in providing information about: (i) association constants; (ii) the exchange rate of Ca2’ (i.e., k,n); (iii) dynamics in the Ca2+ binding site; and (iv) the apparent pK value for the group(s) involved in Ca2+ binding.

Factors regulating the formation of chylomicrons and very-low-density lipoproteins by the rat small intestine

The aim of this study was to investigate how the relationship between chylomicron and very-low-density lipoprotein (VLDL) transport of fatty acid into lymph was affected by the total amount of lipid transported via the intestinal lymphatics in the rat. Two different experimental conditions were employed. First, intestinal lymph fistula rats were infused with four different levels of [3H]oleic acid (15, 30, 60 and 120 mumol per h) at a constant rate for 8 h. Lymphatic transport of [3H]oleic acid via chylomicrons and VLDLs was measured in lymph collected during the seventh h. Within the dose range studied chylomicron increased exponentially, while the output in VLDL reached a plateau at a total lymph [3H]oleic acid output of approx. 60 mumol/h. A linear regression analysis of the ln(chylomicron/VLDL) versus the total output in lymph yielded a coefficient of correlation of 0.95. Second, we utilized the fact that intraduodenal infusion of the nonionic detergent Pluronic L-81 (L-81) inhibits chylomicron transport and that this inhibition is reversed by the cessation of L-81 infusion (unblocking). A linear regression analysis of the ln(chylomicron/VLDL) versus total lymph [3H]oleic acid output during the first 4 h of unblocking gave a coefficient of correlation of 0.79. Statistical analysis of the regression equations from the two experiments showed that for the same lymphatic [3H]oleic acid output, the chylomicron/VLDL ratio was significantly lower in the L-81 experiment, indicating that the relative rates of formation of chylomicron to VLDL were different under these two experimental conditions. However, the principal pattern was the same, i.e., chylomicron production increased, while VLDL production became saturated when the amount of oleic acid transported to the lymph was increased.

Effect of pancreatic phospholipase A2 and gastric lipase on the action of pancreatic carboxyl ester lipase against lipid substrates in vitro

Preincubation of a triolein/phospholipid/cholesteryl oleate-emulsion in vitro with either pancreatic phospholipase A2 (PLA2) or gastric lipase (GL) resulted in hydrolysis (measured by pH-stat-titration) of cholesteryl [3H]oleate only after human pancreatic carboxyl ester lipase (CEL) was added to the system. No appreciable hydrolysis was observed when CEL was added alone. Consequently, a concerted action either of PLA2 and CEL or of GL and CEL made the substrate cholesteryl oleate available for hydrolysis by CEL. This was the case when cholesteryl oleate was solubilised in a phospholipid-stabilised triglyceride emulsion, which is the physico-chemical form in which the major part of dietary cholesteryl esters are presented to the gastro-intestinal tract of man.