The vitamin B6 paradox: Supplementation with high concentrations of pyridoxine leads to decreased vitamin B6 function.

Vitamin B6 is a water-soluble vitamin that functions as a coenzyme in many reactions involved in amino acid, carbohydrates and lipid metabolism. Since 2014, >50 cases of sensory neuronal pain due to vitamin B6 supplementation were reported. Up to now, the mechanism of this toxicity is enigmatic and the contribution of the various B6 vitamers to this toxicity is largely unknown. In the present study, the neurotoxicity of the different forms of vitamin B6 is tested on SHSY5Y and CaCo-2 cells. Cells were exposed to pyridoxine, pyridoxamine, pyridoxal, pyridoxal-5-phosphate or pyridoxamine-5-phosphate for 24h, after which cell viability was measured using the MTT assay. The expression of Bax and caspase-8 was tested after the 24h exposure. The effect of the vitamers on two pyridoxal-5-phosphate dependent enzymes was also tested. Pyridoxine induced cell death in a concentration-dependent way in SHSY5Y cells. The other vitamers did not affect cell viability. Pyridoxine significantly increased the expression of Bax and caspase-8. Moreover, both pyridoxal-5-phosphate dependent enzymes were inhibited by pyridoxine. In conclusion, the present study indicates that the neuropathy observed after taking a relatively high dose of vitamin B6 supplements is due to pyridoxine. The inactive form pyridoxine competitively inhibits the active pyridoxal-5'-phosphate. Consequently, symptoms of vitamin B6 supplementation are similar to those of vitamin B6 deficiency.

Iron Supplements and Magnesium Peroxide: An Example of a Hazardous Combination in Self-Medication.

The use of self-medication, which includes dietary supplements and over-the-counter drugs, is still on the rise, while safety issues are not well addressed yet. This especially holds for combinations. For example, iron supplements and magnesium peroxide both produce adverse effects via the formation of reactive oxygen species (ROS). This prompted us to investigate the effect of the combination of three different iron supplements with magnesium peroxide on ROS formation. Hydroxyl radical formation by the three iron supplements either combined with magnesium peroxide or alone was determined by performing a deoxyribose assay. Free iron content of iron supplements was determined using ferrozine assay. To determine hydrogen peroxide formation by magnesium peroxide, a ferrous thiocyanate assay was performed. Finally, electron spin resonance spectroscopy (ESR) was performed to confirm the formation of hydroxyl radicals. Our results show that magnesium peroxide induces the formation of hydrogen peroxide. All three iron supplements induced the formation of the extremely reactive hydroxyl radical, although the amount of radicals formed by the different supplements differed. It was shown that combining iron supplements with magnesium peroxide increases radical formation. The formation of hydroxyl radicals after the combination was confirmed with ESR. All three iron supplements contained labile iron and induced the formation of hydroxyl radicals. Additionally, magnesium peroxide in water yields hydrogen peroxide, which is converted into hydroxyl radicals by iron. Hence, iron supplements and magnesium peroxide is a hazardous combination and exemplifies that more attention should be given to combinations of products used in self-medication.

Anticholinergic Accumulation: A Slumbering Interaction between Drugs and Food Supplements.

Many compounds display anticholinergic effects which might give rise to cognitive impairment and even delirium. These side effects are caused by their ability to bind to muscarinic receptors in our brain. Especially with combination of compounds, these serious effects are seen. This phenomenon, known as anticholinergic accumulation, is especially seen in the elderly. A classification of drugs for anticholinergic side effects has been made based on clinical observations, the ACB score. Here, we aimed to substantiate this classification by comparing the affinity of numerous drugs for the muscarinic receptors to the ACB score. Additionally, a number of supplements were screened. The affinity of the compounds was determined by their ability to displace the radioligand [(3)H]pirenzepine of the muscarinic receptor induced by these compounds. Our results show that the affinity of a compound for the muscarinic receptors correlated with its ACB score. Also food supplements appeared to bind to these muscarinic receptors. Moreover, several drug-drug, supplement-supplement and supplement-drug combinations had an affinity that is higher than the affinity of single compounds. This explains the phenomenon of anticholinergic accumulation. In conclusion, care should be taken to drug-drug and supplement-drug combinations with respect to anticholinergic accumulation.

The shifting perception on antioxidants: the case of vitamin E and ß-carotene.

Antioxidants are vital for aerobic life, and for decades the expectations of antioxidants as health promoting agents were very high. However, relatively recent meta-analyses of clinical studies show that supplementation of antioxidants does not result in the presumed health benefit, but is associated with increased mortality. The dilemma that still needs to be solved is: what are antioxidants in the end, healthy or toxic? We have evaluated this dilemma by examining the presumed health effects of two individual antioxidants with opposite images i.e. the "poisonous" ß-carotene and the "wholesome" vitamin E and focused on one aspect, namely their role in inducing BPDE-DNA adducts. It appears that both antioxidants promote DNA adduct formation indirectly by inhibition of the protective enzyme glutathione-S-transferase π (GST π). Despite their opposite image, both antioxidants display a similar type of toxicity. It is concluded that, in the appreciation of antioxidants, first their benefits should be identified and substantiated by elucidating their molecular mechanism. Subsequently, the risks should be identified including the molecular mechanism. The optimal benefit-risk ratio has to be determined for each antioxidant and each individual separately, also considering the dose.

The supplement-drug interaction of quercetin with tamsulosin on vasorelaxation.

The food supplement quercetin is used as self-medication for prostate disorders and is known to induce vasorelaxation. The drug tamsulosin is used in the treatment of benign prostatic hyperplasia. A major side effect of tamsulosin is orthostatic hypotension, mediated by vasorelaxation resulting from α1-adrenoceptor blockade. The overlapping profile prompted us to investigate the pharmacodynamic interaction of quercetin with tamsulosin. Since quercetin is extensively metabolized in the intestines and the liver, the metabolites quercetin-3-glucuronide and 4'O-methyl-quercetin were also examined. Vasorelaxation induced by the compounds was tested in rat mesenteric arteries (average diameter: 360±µm) constricted by the α1-adrenoceptor agonist phenylephrine. Tamsulosin (0.1nM) decreased phenylephrine sensitivity 17-fold (n=10). Quercetin (5, 10 and 20µM) also caused a decrease (2-, 4- and 6-fold respectively) of phenylephrine sensitivity, while 10µM of quercetin-3-glucuronide and 4'O-methyl-quercetin decreased this sensitivity (1.5- and 2-fold) only slightly (n=6). The combination of tamsulosin with quercetin or quercetin metabolites proved to be far more potent than the compounds in isolation. The combination of quercetin, quercetin-3-glucuronide or 4'O-methyl-quercetin with tamsulosin decreased the phenylephrine sensitivity approximately 200-, 35- and 150-fold (n=6). The strong pharmacodynamic interaction between the food supplement quercetin and tamsulosin underlines the potential of the impact of supplement-drug interactions that warrant more research.

The effect of vitamin E supplementation on serum DHEA and neopterin levels in elderly subjects.

Contradictory results have been published on the immune-stimulating effects of vitamin E. Using a randomized placebo-controlled design, the effect of 15 month's daily supplementation with 200 mg vitamin E on two biomarkers of immunocompetence, i.e. serum DHEA sulfate ester (DHEA-S) and neopterin, was studied. Of the 100 relatively healthy Dutch elderly subjects included in the study, 50 were supplemented with vitamin E and 50 received placebo. As compared to placebo, vitamin E supplementation affected neither serum DHEA-S nor serum neopterin level. This corroborates with the finding that vitamin E supplementation did not affect infection-related severity measures, i.e. total number of days with respiratory infection, and total duration of the infections. It is concluded that vitamin E supplementation does not substantially alter the immunocompetence markers DHEA and neopterin in elderly subjects, and may explain our recently reported failure of vitamin E supplementation to afford protection against acute respiratory infections.