The PXE Mouse Model and Magnesium


MAY 12, 2010
by Christine Vocke, Director of Education and Information, PXE International
and by Sharon Terry, CEO, PXE International


Research on pseudoxanthoma elasticum (PXE) using knockout (KO) mice models has continued, and there are three interesting studies to report. A PXE KO mouse is a genetically engineered mouse in which the function of the ABCC6 gene is 'knocked out' so that it doesn't function. The PXE KO mouse reliably develops mineralization in elastic and connective tissues that mimics pseudoxanthoma elasticum in humans - and the degree of mineralization can be measured. Their diets and environment are controlled, so they provide a good model on which to test the effects of various treatments on PXE. Several studies have looked at the effects of magnesium and other minerals on the PXE KO mouse. The PXE KO mouse is compared to a wild type (WT) mouse to understand the effect of the gene being turned off. In WT mice all genes function normally.

A study conducted in the Netherlands [1] looked at mineralization in PXE KO mice and WT mice on high and normal calcium (Ca), and high and normal magnesium (Mg) diets. Three diets were tested and mice were kept on them through 3, 7 and 12 months of age. A baseline diet contained the normal amounts of Ca and Mg necessary for mouse growth and health. A 4X-Ca diet contained four times the amount of calcium, but the same amount of magnesium as the baseline diet. A 4X-Ca, 4X-Mg diet contained four times the amount of calcium and four times the amount of magnesium as the baseline diet. Mice were examined for mineralization in their blood vessels and hearts at 3, 7 and 12 months of age.

Only 4 of 58 WT mice developed calcifications. Because there were so few calcifications in WT mice, it was not possible to speculate on potential differences between the diets in WT mice. In contrast, the PXE KO mice readily developed calcifications. The KO mice on the baseline diet already had calcifications after three months, and the number of mice with calcifications increased after 12 months. Calcifications did not increase in the KO mice on the 4X-Ca diet compared to the baseline diet. Calcification was significantly slowed in KO mice fed the 4X-Ca, 4X-Mg diet when compared to the baseline diet or 4X-Ca diet after 3, 7 and 12 months. After 12 months on the 4X-Ca, 4X-Mg diet, the number of KO mice with calcifications was less than one third that in the other diet groups.

This experiment clearly showed that dietary magnesium significantly reduced calcification in this PXE mouse. It also showed that a high calcium diet did not increase the severity of pseudoxanthoma elasticum in the mouse. This study also supports and extends the findings of an earlier study by LaRusso et al. [2] by following the mice on high Mg diets up to 12 months of age.

Another mouse study by Li and Uitto [3] showed that depriving PXE KO mice of magnesium in their diets accelerated the mineralization process. This study also examined the effect of genetic background of the KO mice on the mineralization process. PXE KO mice were crossed with mice that had a single mutation on the GGCX gene. In humans, a single mutation on the GGCX gene causes PXE-like skin manifestations along with a blood coagulation problem. Thus, some of the KO mice also had a mutation on the GGCX gene. Two mouse diets were used and the mice were examined for mineralization. The standard mouse diet contained normal amounts of all minerals and vitamins necessary for mouse health. The experimental diet contained decreased calcium and magnesium. The mineralization process was accelerated in the KO mice with the accompanying GGCX mutation. Mineralization was also accelerated in both groups of mice fed the very low magnesium diet. Furthermore, the KO mice with a GGCX mutation showed a three-fold increase of mineralization on the very low magnesium diet compared to their litter mates on the standard diet. Thus, the genetic background of PXE KO mice also has a profound effect on mineralization.

Finally, a recent article by Li et al. [4] reports results of PXE KO mice treated with two different oral phosphate binders, one of them containing magnesium carbonate. Phosphate binders are drugs that are used to control elevated phosphate levels (hyperphosphatemia) in people with chronic kidney disease. A 2005 study [5] of six patients with pseudoxanthoma elasticum taking an aluminum-containing phosphate binder suggested that three of them showed significant improvement in skin lesions, and all six patients had no deterioration in their eyes during the one year on the drug. Aluminum-containing phosphate binders have been shown to be toxic to humans, so Dr. Li's study looked at two alternate phosphate-binding drugs – lanthanum carbonate and magnesium carbonate.

In this study, WT and PXE KO mice were placed on a standard rodent diet supplemented with either lanthanum carbonate or magnesium carbonate. The magnesium-enriched diet contained five times the concentration of the standard diet. The mice were examined for mineralization at three and six months of age. The lanthanum carbonate-enriched diet did not change the mineralization process in the mice. However, the magnesium carbonate-enriched diet completely prevented mineralization up to six months of age.

Another group of PXE KO mice was fed the standard diet and allowed to develop mineralization up to three months of age, and then was switched to the magnesium-enriched diet and followed for another three months. These six-month old mice showed very little mineralization, comparable to the PXE KO mice on the standard diet at three months of age. Thus, magnesium carbonate arrested the mineralization in these mice and possibly even reversed it.

Because there are some concerns in the medical literature that long-term excessive magnesium supplementation in humans may be harmful to bones, this study also examined the bone density of the six month old mice on the magnesium-enriched diet. There was no negative effect on the bones of the mice on the magnesium-enriched diet – in fact, some of the findings suggest that magnesium intake may be beneficial to bones.

What do these mouse studies have to do with people affected by pseudoxanthoma elasticum? It is clear that diets high in magnesium completely prevent mineralization in PXE mice up to 12 months of age. The Li study [4] tested this effect with magnesium carbonate, a drug that is approved for clinical use in humans. The Li and Uitto study [3] showed that the genetic background of mice (and by inference, of people with PXE) profoundly influences the mineralization process and that magnesium deprivation accelerates mineralization. Dr. Jouni Uitto, a member of PXE International´s Professional Advisory Board, says that the role of magnesium (and other dietary molecules such as vitamin K) should be carefully examined in controlled clinical trials in humans [6]. Unfortunately, such studies may be difficult to set up because of the slow progress of PXE in humans, and a lack of measurable markers of the progression of PXE in humans. Furthermore, anecdotally, many people affected with pseudoxanthoma elasticum are already supplementing their diet with magnesium and /or with vitamin K, and would most likely be excluded from such a trial.

Dr. Li notes in her discussion [4] that dietary magnesium and its role in control of mineralization may be important beyond PXE. She also notes that a National Health and Nutrition Examination Survey 1999-2000 [7] concluded that substantial numbers of US adults failed to consume adequate amounts of magnesium in their diets. However, in most of the mouse studies, the amount of magnesium the mice consumed was much more than is recommended for humans. Thus, Dr. Uitto and other advisors for PXE International caution that we need human clinical studies before any recommendation can be made. Because mice showed that genetic background is also important, and because the genetic background of humans is so varied, we have no idea yet about treatments for humans.

The NIH Office of Dietary Supplements has published fact sheets on drugs, supplements and herbs. (http://ods.od.nih.gov/)  The following information is from the fact sheet on magnesium. Dark green vegetables, some legumes, nuts and seeds, and whole, unrefined grains are good sources of magnesium.

Recommended Dietary Allowances for magnesium
for children and adults

http://ods.od.nih.gov/factsheets/magnesium.asp
 

 Age
Years

Male
mg/day 

Female
mg/day 

Pregnancy
mg/day 

Lactation
mg/day 

1-3

80 

80

N/A 

N/A

4-8

130

130

N/A 

N/A

9-13

240

240

N/A

N/A

14-18

410

360 

400 

360 

19-30 

400

310

350 

310

31+

420 

320 

360 

320

 


References


[1] Gorgels T, Waarsing JH, de Wolf A, ten Brink JB, Loves WJP, Bergen AAB, Dietary magnesium, not calcium, prevents vascular calcification in a mouse model for pseudoxanthoma elasticum, J Mol Med, published online (Mar 19, 2010). PMID: 20177653

[2] LaRusso J, Li Q, Jiang Q, Uitto J, Elevated Dietary Magnesium Prevents Connective Tissue Mineralization in a Mouse Model of Pseudoxanthoma Elasticum (Abcc6-/-), J Invest Dermatol 129, 1388 (Jun 2009) Patient Summary

[3] Li Q, Uitto J, The mineralization phenotype in Abcc6-/- mice is affected by Ggcx gene deficiency and genetic background - a model of pseudoxanthoma elasticum, J Mol Med 88, 173 (2010). PMID: 19784827

[4] Li Q, LaRusso J, Grand-Pierre AE, Uitto J, Magnesium Carbonate-Containing Phosphate Binder Prevents Connective Tissue Mineralization in Abcc6-/- Mice - Potential for Treatment of Pseudoxanthoma Elasticum, CTS Journal 2, 398 (Dec 2009). PMID: 20443931

[5] Sherer DW, Singer G, Uribarri J, LPhelps R, Sapadin AN, Bailey Freund K, Yannuzzi L, Fuchs W, Lebwohl M, Oral phosphate binders in the treatment of pseudoxanthoma elasticum, J Am Acad Dermatol 5, 610 (2005). PMID: 16198780

[6] Uitto J, personal communication (Apr 15, 2010)

[7] Ford ES, Mokdad AH, Dietary Magnesium Intake in a National Sample of U.S. Adults, J Nutr 133, 2879 (2003). PMID: 12949381