H.J.M. van Rijn

Oral magnesium supplementation in insulin-requiring Type 2 diabetic patients.

Oral magnesium (Mg) supplementation can improve insulin sensitivity and secretion in patients with Type 2 diabetes mellitus (DM). We studied the effect of Mg supplementation on glycaemic control, blood pressure, and plasma lipids in insulin‐requiring patients with Type 2 DM. Fifty moderately controlled patients were randomized to 15 mmol Mg or placebo daily for 3 months. Plasma Mg, glucose, HbA1c, lipids, erythrocyte Mg, Mg and glucose concentrations in 24‐h urine, and systolic and diastolic pressure were measured before and after 3 months treatment. Plasma Mg concentration was higher after supplementation than after placebo (0.82 ± 0.07 vs 0.78 ± 0.08 mmol l−1, p<0.05), as was Mg excretion (5.5 ± 1.9 vs 3.7 ± 1.4 mmol 24 h−1, p = 0.004) but erythrocyte Mg concentrations were similar. No significant differences were found in glycaemic control (glucose: 10.7 ± 3.8 vs 11.6 ± 6.2 mmol l−1, p = 0.8; HbA1c: 8.9 ± 1.6 vs 9.1 ± 1.2%, p = 0.8), lipids or blood pressure. On‐treatment analysis (34 patients: 18 on Mg, 16 on placebo) yielded similar results. An increase in plasma Mg concentration irrespective of medication was associated with a tendency to a decrease in diastolic pressure (increased plasma Mg vs no increase: −4.0 ± 10.1 vs +2.5 ± 12.0 mmHg, p = 0.059). Three months’ oral Mg supplementation of insulin‐requiring patients with Type 2 DM increased plasma Mg concentration and urinary Mg excretion but had no effect on glycaemic control or plasma lipid concentrations.

Effect of sodium fluoride on the prevention of corticosteroid-induced osteoporosis

To investigate whether sodium fluoride (NaF) is able to prevent bone loss in patients treated with corticosteroids (Cs), we performed a randomized, double-masked, placebo-controlled trial with 44 Cs-treated patients without established osteoporosis, defined as the absence of previous peripheral fractures and vertebral deformities on radiographs. The effects of NaF (25 mg twice daily) and placebo on the bone mineral density (BMD) of the lumbar spine and hips were compared at baseline and at 6, 12, 18 and 24 months. After 2 years, the BMD of the lumbar spine had decreased in the placebo group by 3.0% (95% CI: −4.9% to −1.0%;p<0.01); in the NaF group there was a statistically insignificant increase in BMD of 2.2% (95% CI: −0.8% to +5.3%). The difference in the changes in BMD between the two groups was +5.2% (95% CI: +1.8% to +8.6%;p<0.01). In the hips, BMD had decreased after 2 years in both groups: in the placebo group by −3.0% (95% CI: −5.0% to −1.0%;p<0.05) and in the NaF group by 3.8% (95% CI: −6.1% to −1.5%;p<0.01). The difference in the changes in BMD between the two groups was not significant: +0.8% (95% CI: −2.1% to +3.8%). Three vertebral deformities were observed in the placebo group and one in the NaF group (insignificant difference), while no peripheral fractures occurred during the study period. It is concluded that in Cs-treated patients without established osteoporosis NaF prevents bone loss in the lumbar spine but does not have a positive effect on the BMD of the hips.

Apolipoprotein(a) isoform size influences binding of lipoprotein(a) to plasmin-modified des-AA-fibrinogen

Abstract Lipoprotein(a) (Lp(a)) is a LDL-like particle with an additional glycoprotein, apo(a), linked to apolipoprotein B-100. Apo(a) is highly homologous to parts of the plasminogen molecule, and numerous investigations have shown interference of Lp(a) with functions of plasminogen. In this report we studied the influence of apo(a) phenotype on the binding of Lp(a) to plasmin-modified immobilized des-AA-fibrinogen (desafib-X). Results indicate that Lp(a) binds to desafib-X in a specific and saturable way. There was a strongly significant negative correlation between apo(a) isoform length and maximal number of Lp(a) particles bound to the desafib-X matrix (N=18, r=0.84, p=0.002). There was no relation between apo(a) isoform length and K d for the binding of Lp(a) to desaflb-X. In two donors (10%) no specific binding to desafib-X was observed, as well as to lysine-sepharose. In conclusion, apo(a) isoform length influences the amount of Lp(a) binding to desaflb-X. This implies that small isoforms apart from their usual higher plasma Lp(a) concentrations also are potentially more thrombogenic. The fact that Lp(a) from two donors did not bind to desafib-X, suggests that mutations may exist in the K4-10 domain of apo(a) abolishing its lysine-binding ability.

Kinetic analysis of lipoprotein (a) inhibition of plasminogen activation by tissue plasminogen activator in vitro

Abstract Lipoprotein (a) (Lp(a)) is recognised as an independent risk factor for atherosclerosis. Lp(a) consists of a LDL-like moiety with an additional protein, apo(a), bound to the apolipoprotein B-100. This apo(a) has a high homology with plasminogen (Pg). This prompted us to investigate The possible interference of Lp(a) with Pg activation in vitro. We purified Lp(a) with sequential ultracentrifugation followed by affinity chromatography using lysine-sepharose. Different concentrations of Lp(a) were added to a mixture of Pg, t-PA and CNBr-digested fibrinogen. The plasmin formation was quantified with a plasmin specific substrate S-2251. The experiments indicate that Lp(a) inhibits the rate of plasmin formation in a concentration dependent way with an uncompetitive inhibition constant Kiu = 38 nM. Experiments with varying amounts of fibrinogen fragments show that these fragments are imperative for the inhibition of the Pg activation by Lp(a). Excess of these fragments attenuates the inhibition. This suggests that Lp(a) inhibits Pg activation through the formation of a Lp(a)-fibrin(ogen) complex.

Absolute bioavailability of fluoride from disodium monofluorophosphate and enteric-coated sodium fluoride tablets

Objectives: The absolute bioavailability and other pharmacokinetic parameters of two fluoride formulations were investigated in 13 healthy volunteers, aged 61–70 years.Methods:The following formulations were administered, under fasting conditions, in a single-dose three-way cross-over design: tablets of 76 mg disodium monofluoro phosphate (MFP, equivalent to 10.0 mg F− ion), enteric-coated (e.c.) tablets of 25 mg sodium fluoride (NaFor, equivalent of 11.3 mg F− ion), and an isoosmotic aqueous injection solution (4 ml) of 22.1 mg sodium fluoride (NaFiv, equivalent of 10.0 mg F− ion). There was a wash-out period of at least one week between each administration. Blood was sampled before and during a 24-hour period after administration. For F− excretion urine was sampled 48 hours before (baseline) and over the 48 hours after the adminstration.Results:The mean t1/2 values of the three formulations were 8.3, 8.7 and 8.3 h for MFP, NaFor and NaFiv respectively, and were not significant different. Mean Cmax after MFP was significantly higher than after NaFor [344 vs 142 μg⋅l−1]. Mean tmax for MFP was shorter than for NaFor [1.1 vs 4.6 h]. MFP had significantly higher bioavailability [102.8%] than NaFor [64.2%].Conclusion:The MFP formulation showed higher bioavailability with smaller variation than the NaFor formulation. MFP is preferable, therefore, for fluoride therapy in clinical practice, and changing from NaFor to MFP will require adjustment of the dose.

Differentiation of the roles of the apolipoprotein(a) and LDL moiety in the binding of lipoprotein(a) to limited plasmin digested des AA fibrin

Summary Elevated plasma levels of lipoprotein (a) (Lp(a)) in humans represent a major inherited risk factor for atherosclerosis. Lp(a) consists of a LDL-like particle with an additional glycoprotein, apolipoprotein(a) (apo(a)), linked to apolipoprotein B100. The apo(a) moiety is highly homologous to plasminogen as it contains multiple repeats resembling plasminogen kringle IV, a lysine and fibrin binding domain. In the present study, the individual contribution of the two constituents of Lp(a), namely LDL and apo(a), in the binding of Lp(a) to limited plasmin digested des AA fibrin (Desafib-X) is examined. Lp(a) was isolated by sequential ultracentrifugation followed by gel filtration chromatography. Lysine binding (Lp(a)lys+) and non-lysine binding (Lp(a)lys−) Lp(a) were obtained by affinity chromatography using lysine-Sepharose. Lp(a)-free LDL was isolated by ultracentrifugation followed by Lp(a)-free LDL was isolated by ultracentrifugation followed by chromatofocusing. 125I-labelled Lp(a), LDL, Lp(a)lys−, and Lp(a)lys+ preparations were incubated with Desafib-X coated wells in the presence or absence of ɛ-aminocaproic acid (ɛACA, a lysine-analogue) and/or autologous LDL. Total Lp(a) contained 86±8% Lp(a)lys+. The mean apparent dissociation constant (Kd in nM) for Lp(a), LDL, Lp(a)lys−, and Lp(a)lys+ binding to Desafib-X was 48±11, 28±4, 7±4, and 43±23, respectively. The binding of Lp(a) and Lp(a)lys+ to Desafib-X could be inhibited to a similar degree by 0.2m ɛACA (for 31±14% and 37±15% respectively), indicating lysine specific binding of these preparations. The binding of Lp(a)lys− and LDL could not be inhibited by ɛACA. A ten times molar excess of LDL could inhibit the binding of Lp(a), Lp(a)lys−, and Lp(a)lys+ to Desafib-X by 60 to 80%. For Lp(a) and Lp(a)lys+, an additional binding-inhibition can be observed when adding 0.2M ɛACA. In conclusion, the overall findings indicate that the binding of Lp(a) to fibrin(-ogen) is more complex than previously thought and imposes an influence of the LDL moiety and LDL, additional to the apo(a) moiety, in the binding of Lp(a) to lysine-containing proteins like Desafib-X.

Method-dependent increase in lipoprotein(a) in insulin-dependent diabetes mellitus during pregnancy

The current prevalent view is that plasma lipoprotein(a) [Lp(a)] concentrations are under strong genetic control. Most dietary and drug interventions seem to have little or no effect on plasma Lp(a) levels. However, evidence for a possible regulatory rol e of hormones is accumulating, for instance, fluctuations of Lp(a) levels during pregnancy have been reported. Also, in insulin-dependent diabetes mellitus (IDDM) patients, elevated Lp(a) levels have been reported. In the present longitudinal study, plasma lipid concentrations, including Lp(a), were determined in IDDM women before pregnancy, during pregnancy, and 3 months postpartum. In our study population, Lp(a) concentration was not significantly correlated with either hemoglobin A1c (HbA1c) levels of apolipoprotein(a) [apo(a)] phenotype. Changes in other lipid parameters observed during pregnancy in our IDDM population were similar to those reported during normal pregnancy. Lp(a) concentrations were quantified using two different immunochemical methods that possess different sensitivities and specificities: an immunoradiometric assay (IRMA) using two different anti-apo(a) antibodies, and an enzyme-linked immunosorbent assay (ELISA) using an anti-apo(a) and an anti-apo B antibody. Median prepregnancy Lp(a) concentrations were 118 mg/L (range, 15 to 672) as determined with the IRMA and 107 mg/L (range, 21 to 451) as determined with the ELISA. Women with IDDM showed, in general, no significant change in Lp(a) concentration during pregnancy when it was assayed with the IRMA, although a tendency to increased values was observed. When Lp(a) concentrations were determined with the ELISA, a strong and significant increase in Lp(a) from weeks 17 to 24 of pregnancy onward was found. The latter results confirm the prevalent view that during pregnancy Lp(a) levels are increased. However, the present results and those of others and Lp(a) in normal pregnancy strongly emphasize the importance of method selection when determining Lp(a) concentrations.