Vitamin K and phosphate mediated enhancement of brain sulfotransferase activity

Tocopherol Moderately Induces the Expressions of Some Human Sulfotransferases, which are Activated by Oxidative Stress

Oxidative stress is generated in biological system by several endogenous/exogenous factors like environmental-pollution/toxicity/diseases and by daily-life-stress. We previously showed that oxidative-stress impaired the activities/expressions of phase-II drug-metabolizing enzyme, sulfotransferases (SULTs). The SULT catalyzes sulfation of endogenous/exogenous compounds. Vitamin E is globally consumed by a large number of individuals for the cellular protection from oxidative stress and aging. Here, vitamin E (tocopherol; α/γ and tocotrienol; α/γ; 0, 1, 10, or 100 μM) was tested in human carcinoma cell line, HepG2 for their influences on SULTs expression/(western blotting). The effects of oxidant (glutathione-oxidized/GSSG) or reductant (glutathione-reduced/GSH, Dithiothreitol/DTT) on SULT activities were studied in rat-liver/human intestinal tissues. Results suggest, tocopherol is more inductive to monoamine-SULT (MPST) and Dehydroepiandrosterone-SULT (DHEAST) compared to that of tocotrienol (inconsistent change in PPST, phenol sulfotransferase/MPST/EST, estrogen sulfotransferase). The nuclear-factor constitutive androstane receptor (CAR) was found to be induced moderately. This study overall describes that vitamin E moderately influences SULTs expression. The induction ability of tocopherol should be judged taking into account its long-term consummation. Oxidative stress activates rat and human SULTs activities and expressions. Further studies are necessary in this regard.

Effects of Long-term Vitamin K (Phylloquinone) Intake on Retina Aging

Emerging evidence suggests neuroprotective functions of vitamin K and/or vitamin K-dependent proteins. We investigated the effect of dietary vitamin K on retina aging (thinning). Female Sprague-Dawley rats were maintained from weaning on low (80 microg kg(-1) diet), adequate (500 microg kg(-1) diet) or high (2000 microg kg(-1) diet) levels of vitamin K1 (phylloquinone). Relative concentrations of brain vitamin K associated with these diets were 1: 3.3: 25 (K1) and 1: 2.7: 9.0 (menaquinone-4). Histomorphometry of old (21 month) rats revealed positive associations between vitamin K and thickness of retina layers, especially in the equatorial/peripheral retina. No association of diet and retina thickness was detected among young (6 month) animals. The sparing effect of vitamin K in the retina was most evident in the inner plexiform layer and in the photoreceptor inner and outer segments. Surprisingly, we observed no effect of vitamin K on the age-dependent loss of photoreceptor cells, interneurons or ganglion cells. These data suggest a role for vitamin K in maintaining the aging retina and suggest that the sparing effect of vitamin K does not reflect the survival-promoting (anti-apoptotic) activities of vitamin K-dependent proteins.

Vitamin k antagonist warfarin for palliative treatment of metachromatic leukodystrophy, a compassionate study of four subjects

MLD is characterized by accumulation of sulfatides in the brain. Vitamin K regulates two enzymes in sphingolipid biosynthesis and warfarin is known to lower brain sulfatides in rats and mice. We hypothesized that warfarin may mitigate the MLD phenotype by reducing the formation of sulfatides. This compassionate study recruited four advanced patients with clinical, biochemical and genetic confirmation of MLD. The patients were treated with warfarin according to the approved protocol for a total of 45 days. The battery of tests included proton MR spectroscopy (H-MRS) of brain and urinary sulfatide levels recorded at defined intervals. The patients tolerated the medication and there were no bleeding complications.

The urinary sulfatide levels did not decline during the study period. The H-MRS showed decreased N-acetyl aspartate and elevated myoinositol levels in the basal ganglia which remained unchanged after treatment.

Our study did not demonstrate any beneficial effects of warfarin in four advanced cases of MLD. The drug intervention however, was safe and deserves further evaluation through a larger study of longer duration. The metabolite abnormalities reported on H-MRS may be useful in longitudinal follow up of patients with MLD during drug trials.

Vitamin K and the nervous system: an overview of its actions

The role of vitamin K in the nervous system has been somewhat neglected compared with other physiological systems despite the fact that this nutrient was identified some 40 y ago as essential for the synthesis of sphingolipids. Present in high concentrations in brain cell membranes, sphingolipids are now known to possess important cell signaling functions in addition to their structural role. In the past 20 y, additional support for vitamin K functions in the nervous system has come from the discovery and characterization of vitamin K-dependent proteins that are now known to play key roles in the central and peripheral nervous systems. Notably, protein Gas6 has been shown to be actively involved in cell survival, chemotaxis, mitogenesis, and cell growth of neurons and glial cells. Although limited in number, studies focusing on the relationship between vitamin K nutritional status and behavior and cognition have also become available, pointing to diet and certain drug treatments (i.e., warfarin derivatives) as potential modulators of the action of vitamin K in the nervous system. This review presents an overview of the research that first identified vitamin K as an important nutrient for the nervous system and summarizes recent findings that support this notion.

Lifelong low-phylloquinone intake is associated with cognitive impairments in old rats

In a previous report, we showed vitamin K to preferentially accumulate in brain regions rich in white matter and to positively correlate with certain sphingolipids. In rodents, pharmacological vitamin K deficiency has resulted in behavioral perturbations. To gain insight on the role of vitamin K status on brain function, we investigated learning abilities (Morris water maze), motor activity (open field), and anxiety (elevated plus maze) in distinct groups of 6-, 12-, and 20-mo-old female Sprague-Dawley rats that had been fed diets containing low (L; ~80 μg/kg diet), adequate (A; ~500 μg/kg diet), or high (H; ~2000 μg/kg diet) levels of phylloquinone (μg/kg diet; n = 9-12/diet) since weaning. In 20-mo-old rats, sphingolipids (cerebroside, sulfatide, sphingomyelin, ceramide, and gangliosides), phylloquinone, and menaquinone-4 were also assessed in cerebellum, midbrain, pons medulla, striatum, and hippocampus. Lifetime consumption of a low-vitamin K diet resulted in cognitive deficits in the 20-mo-old rats, with those in the L group having longer latencies than those in the H group (P < 0.05); this was associated with higher concentrations of ceramides in the hippocampus (P < 0.05) and lower gangliosides in the pons medulla and midbrain (P < 0.05). The low-vitamin K diet did not affect cognition at 6 and 12 mo of age, nor did it affect motor activity or anxiety at any age. Although much remains to be elucidated about the mechanism of action of vitamin K in cognition, this report points to vitamin K as an important nutritional factor contributing to cognitive health during aging.

Vitamin K and sphingolipid metabolism: evidence to date

The brain is enriched with sphingolipids, which are important membrane constituents and major lipid signaling molecules that have a role in motor and cognitive behavior. Vitamin K has been implicated in brain sphingolipid metabolism for more than 30 years. The in vitro and in vivo studies to date suggest a role of vitamin K in the regulation of multiple enzymes involved in sphingolipid metabolism within the myelin-rich regions in the brain. However, the precise mechanisms of action are not well understood. Further, the physiological consequences of the observed effects of vitamin K on sphingolipid metabolism have not been systematically studied.

Neurological outcome in school-age children after in utero exposure to coumarins

The effect of prenatal exposure to coumarins (acenocoumarol, phenprocoumon) on neurological outcome was assessed in a cohort of 306 children aged 7-15 years. Findings were compared with those in a non-exposed cohort of 267 children, matched for sex, age, and demographic region. We used a neurological examination technique which pays special attention to minor neurological dysfunction (MND). None of the children was found to be neurologically abnormal. However, exposure to coumarins during gestation increases the risk for MND in children of school age, odds ratio (OR) 1.9 (CI(95) 1.1-3.4), predominantly after exposure in the second or third trimester, odds ratio 2.1 (CI(95) 1.2-3.8). We found a dose-response relationship with an odds ratio of 1.2 (CI(95) 1.0-1.5) per mg coumarin derivative prescribed per day. The results suggest that coumarins have an influence on the development of the brain which can lead to mild neurological dysfunctions in children of school age.

Pyridoxal 5'-phosphate binds to a lysine residue in the adenosine 3'-phosphate 5'-phosphosulfate recognition site of glycolipid sulfotransferase from human renal cancer cells

In the course of characterization of glycolipid sulfotransferase from human renal cancer cells, the manner of inhibition of sulfotransferase activity with pyridoxal 5'-phosphate was investigated. Incubation of a partially purified sulfotransferase preparation with pyridoxal 5'-phosphate followed by reduction with NaBH4 resulted in an irreversible inactivation of the enzyme. When adenosine 3'-phosphate 5'-phosphosulfate was coincubated with pyridoxal 5'-phosphate, the enzyme was protected against this inactivation. Furthermore, pyridoxal 5'-phosphate was found to behave as a competitive inhibitor with respect to adenosine 3'-phosphate 5'-phosphosulfate with a Ki value of 287 microM. These results suggest that pyridoxal 5'-phosphate modified a lysine residue in the adenosine 3'-phosphate 5'-phosphosulfate-recognizing site of the sulfotransferase.

A neutral galactocerebroside sulfate sulfatidase from mouse brain

We have described an enzyme in brain that catabolizes galactocerebroside sulfatide with a pH optimum of 7.2. To our knowledge, this is the first description of a catabolic enzyme for sulfatide at a neutral pH. Activity at a neutral pH implies a non-lysosomal location for this sulfatidase. Galactocerebroside sulfate sulfatidase (n-sulfatidase) activity was not apparent in crude microsomal extracts and was detected following partial purification of the enzyme. This enzyme, n-sulfatidase, differs from other arylsulfatases in its M(r), inability to bind to concanavalin A, and substrate specificity; n-sulfatidase was unable to hydrolyze p-nitrocatechol sulfate or estrone sulfate. The molecular mass of n-sulfatidase obtained by Sephacryl S-200 chromatography was 72 kDa, and the active fraction from this procedure was purified > 600-fold by isoelectric focusing. Following SDS-polyacrylamide gel electrophoresis, two bands were obtained with apparent molecular masses of 58 and 66 kDa. Enzyme activity was regenerated from both of these bands, with the 66-kDa band showing greater activity. The Km of the sulfatidase was determined as 5.8 x 10(-5) M. The pI of n-sulfatidase was 7.7 in contrast to the pI of 4.9 for the sulfotransferase. No requirement was found for Mg2+ or ATP for sulfatidase activity; vitamin K1 enhanced sulfatidase activity approximately 3.3-fold. Therefore, this enzyme may have a role in the pathogenesis of metachromatic leukodystrophy in which sulfatides accumulate in the nervous and other tissues and in myelination since sulfatides are an important component of myelin.

Inhibition of phenol sulfotransferase by pyridoxal phosphate

The biologically abundant cofactor, pyridoxal-5-phosphate (PLP), is a potent inhibitor of bovine phenol (aryl) sulfotransferase (PST). Preincubation of purified enzyme with as little as 1 microM PLP decreased PST activity by 50%. Excess 2-naphthol protected PST from inactivation by PLP, whereas 2-naphthyl sulfate and PAPS were not protective. Although PLP inhibition was apparently competitive with 2-naphthol, a steady-state kinetic Ki value could not be measured due to non-linear Lineweaver-Burk plots in the presence of the inhibitor. Kinetic progress curves revealed that this was due to progressive loss of activity during catalysis. The kinetics of inactivation of PST by PLP were pseudo-first-order and exhibited saturation. The derived KI value for the binding of PLP to PST in the initial reversible step was 23 microM, with a maximal rate of inactivation of 0.077 min(-1). Absorbance spectra of the PST/PLP complex indicated the formation of a Schiff base conjugate, and this is consistent with decreased electrophoretic mobility of the protein-PLP adduct in the presence of dodecyl sulfate only after reduction with borohydride. These results point to the possible regulation of an important detoxification enzyme by a ubiquitous cofactor.