Vitamin K Does Not Prevent Mineralization in the PXE Mouse

APRIL 28, 2011
By Christine Vocke, Director of Education and Information, PXE International

Recent scientific evidence has strongly suggested pseudoxanthoma elasticum (PXE) is a metabolic disease. The metabolic hypothesis states that PXE is caused by some substance, or the lack of some substance, that circulates through the whole body. Specifically, researchers now believe that the malfunctioning ABCC6 gene causes a ‘pump’ in cells in the liver to break down. The broken pump then does not transport a substance out of the liver cells and into the blood stream, where it would normally circulate. (See Clear Evidence: PXE Is a Metabolic Disease, and Parabiotic Mouse Pairing Experiments: More Evidence that PXE Is a Metabolic Disease).

PXE researchers have been trying to identify the substance, called a substrate, that is not present in the circulation, which could prevent mineralization. One researcher, Piet Borst, suggested that the substance might be a form of vitamin K. Dr. Borst published his vitamin K hypothesis in June 2008 (1). (See Vitamin K Precursor Might be Involved in PXE).

In February 2011, Dr. Qiujie Jiang and others in Dr. Uitto’s group published the results of a study of vitamin K in mice with pseudoxanthoma elasticum. It was published in the journal Cell Cycle, and is titled “Administration of vitamin K does not counteract the ectopic mineralization of connective tissues in Abcc6 (-/-) mice, a model for Pseudoxanthoma elasticum.”(2)

Dr. Jiang used PXE knockout (KO) mice to test the effects of administration of vitamin K on mineralization in PXE KO mice. A PXE KO mouse is a genetically engineered mouse in which both copies of the ABCC6 gene are ‘knocked out’ so that they do not function, similar to a human with pseudoxanthoma elasticum. The PXE KO mouse reliably develops a late onset of mineralization in various tissues. The PXE KO mouse mimics PXE in humans, and the degree of mineralization can be measured by examination of the muzzle skin of the mouse. The PXE KO mouse is compared to a wild type (WT) mouse. In WT mice, all genes function normally.

The experiments were designed to study the effect of administration of two different forms of vitamin K on the mineralization process in the PXE mouse.

For the first set of experiments, an experimental diet (K2 diet) was formulated that contained 440 times the amount of vitamin K2 than in the baseline mouse diet. The concentration of vitamin K2 in the K2 diet is also nearly 375 times the amount recommended for humans. Three groups of mice were used. One group of PXE KO mice were fed the baseline diet. A second group of PXE KO mice were fed the K2 diet. A third group of WT mice were fed the baseline diet.

After 8 weeks on the diets, the KO mice on the K2 diet had significantly elevated vitamin K levels in their blood and in their livers, compared to the KO and WT mice on the baseline diet. Measurements of mineralization showed that WT mice on the baseline diet had no mineralization, and KO mice on the baseline diet had a significant degree of mineralization. However, KO mice on the K2 diet showed the same degree of mineralization as the KO mice on the baseline diet. So supplementation with vitamin K2 in the diet of mice with pseudoxanthoma elasticum did not alter the mineralization process.

Another form of vitamin K called K3-GSH was also tested. This is a vitamin K derivative, and must be delivered directly into the bloodstream. In an experiment designed to see if this form would halt mineralization, PXE KO mice received IV injections of K3-GSH twice a week for eight weeks. Another group of PXE KO mice received IV injections of saline solution twice a week for eight weeks. The mineralization in both groups of mice was the same – both groups showed significant mineralization typical of PXE KO mice at that age.

Finally, both IV injection and dietary forms of vitamin K, K2, and K3-GSH were tested in three different concentrations in cell cultures in the lab (in vitro). The in vitro system has been used by other researchers to test the effectiveness of other compounds that were thought to interfere with mineralization, such as fetuin-a and magnesium. In this case, neither K2 nor K3-GSH had any effect on the mineralization of the cells in the in vitro system.

These results suggest that administration of vitamin K does not appear to affect mineralization in PXE KO mice.

Read the article abstract.

1.  Piet Borst, Koen van de Wetering and Reinier Schlingemann. Does the absence of ABCC6 (Multidrug Resistance Protein 6) in patients with Pseudoxanthoma elasticum prevent the liver from providing sufficient vitamin K to the periphery? Cell Cycle, 2008 7, 1575 – 1579

2.  Jiang Q, Li Q, Grand-Pierre AE, Schurgers LJ, Uitto J. Administration of vitamin K does not counteract the ectopic mineralization of connective tissues in Abcc6 (-/-) mice, a model for pseudoxanthoma elasticum. Cell Cycle. 2011 Feb 15;10(4):701-7. Epub 2011 Feb 15.