Sapropterin (BH4) aggravates autoimmune encephalomyelitis in mice

Katja Schmitz¹, Sandra Trautmann¹, Lisa Hahnefeld¹, Caroline Fischer¹, Yannick Schreiber¹, Robert Brunkhorst², Ernst R. Werner³, Katrin Watschinger³, Sabine Wicker⁴, Dominique Thomas¹, Gerd Geisslinger^1,5,6, Irmgard Tegeder¹

¹Institute of Clinical Pharmacology, Goethe-University, Medical Faculty, Frankfurt, Germany

²Department of Clinical Neurology, Goethe-University, Medical Faculty, Frankfurt, Germany

³Institute of Biological Chemistry, Biocenter, Medical University of Innsbruck, Austria

⁴Occupational Health Services, Goethe-University, Medical Faculty, Frankfurt, Germany

⁵Fraunhofer Institute for Molecular Biology and Applied Ecology, Branch Translational Medicine, Frankfurt, Germany

⁶Fraunhofer Cluster of Excellence for Immune mediated Diseases, Frankfurt, Germany

Correspondence

Irmgard Tegeder, MD

Goethe-University Frankfurt, Medical Faculty

Institute of Clinical Pharmacology

Theodor Stern Kai 7, 60590 Frankfurt, Germany

Ph 49 696301 7621

tegeder@em.uni-frankfurt.de

Key words

Tetrahydrobiopterin, T-cells, GTP cyclohydrolase, nitric oxide, ceramides, omega lipids

Running head

BH4 and EAE

Word count

Abstract: 247

Main body without Methods/References: 2513

Main body without References: 5170

Abstract

Background and Purpose: Depletion of the enzyme cofactor, tetrahydrobiopterin (BH4) in T-cells was shown to prevent their proliferation upon receptor stimulation in models of allergic inflammation in mice suggesting that BH4 drives autoimmunity. Hence, the clinically available BH4 medication (sapropterin) might increase the risk of autoimmune diseases.

Experimental Approach: The present study assessed the implications for multiple sclerosis (MS) as a model autoimmune disease in MS patients and in immunization-evoked autoimmune encephalomyelitis (EAE), a model of multiple sclerosis in mice.

Key Results: Plasma levels of biopterin were persistently low in MS patients, and the bypass product, neopterin tended to be increased suggesting a relative deficiency of BH4. Ex vivo stimulation of human whole blood indeed led to a drop of biopterin pointing to high consumption. Hence, BH4 replenishment might either further drive the immune response or beneficially restore the BH4 balance. To answer this question, mice were treated with sapropterin in the EAE model. Sapropterin-treated mice had higher EAE disease scores associated with higher numbers of T-cells infiltrating the spinal cord, but normal T-cell subpopulations in spleen and blood, suggesting that BH4 facilitated the invasion of the central nervous system (CNS). Sapropterin-treated EAE mice had increased plasma levels of long-chain ceramides and low levels of the poly-unsaturated fatty acid, linolenic acid (FA18:3). These lipid changes are known to contribute to disruptions of the blood brain barrier in EAE mice.

Conclusion and Implications: Sapropterin might aggravate autoimmune disease of the CNS through permissive effects at the brain barrier.

Abbreviations

AGMO, alkyglycerol monooxygenase; BBB, blood brain barrier; BH4, tetrahydrobiopterin; EAE, experimental autoimmune encephalomyelitis; DAHP, diaminohydroxypyrimidine; GCH1, GTP cyclohydrolase 1; MS, multiple sclerosis; NOS, nitric oxide synthase; RRMS, relapsing remitting MS; PPMS, primary progressive MS; SPMS, secondary progressive MS; PTPS, 6-pyrovoyltetrahydropterin synthase; SPR, sepiapterin reductase