Prolonged 25-OH Vitamin D Deficiency Does Not Impair Bone Mineral Density in Adult Patients With Vitamin D 25-Hydroxylase Deficiency (CYP2R1).

Vitamin D-dependent rickets type 1B (VDDR1B) is an autosomal semidominant genetic disorder caused by a deficiency in CYP2R1, which encodes vitamin D 25-hydroxylase, an enzyme that plays a crucial role in the conversion of vitamin D to 25-dihydroxyvitamin D3. VDDR1B is a severe form of rickets that occurs during infancy and which is responsive to 25-OH vitamin D supplementation. We studied three adult patients from a multi-consanguineous family with VDDR1B. They have been diagnosed with pseudo-nutritional rickets and treated during their adolescence with 25-OH vitamin D. These patients stopped their treatments at the end of adolescence and were contacted 14 to 17 years later when VDDR1B diagnosis was carried out in their niece and nephews. These three patients had undetectable 25-OH vitamin D, but normal levels of plasma 1-25(OH)2 vitamin D. All patients had a hip bone mineral density and a normal vertebral despite osteoarthritis degenerative lesions which may impact BMD evaluation. These findings show that vitamin D supplementation has a questionable effect, if any, for osteoporosis prevention in adulthood in contrast to its crucial importance during infancy and adolescence.

Host CYP27A1 expression is essential for ovarian cancer progression.

There is an urgent need for more effective strategies to treat ovarian cancer. Elevated cholesterol levels are associated with a decreased progression-free survival time (PFS) while statins are protective. 27-Hydroxycholesterol (27HC), a primary metabolite of cholesterol, has been shown to modulate the activities of the estrogen receptors (ERs) and liver x receptors (LXRs) providing a potential mechanistic link between cholesterol and ovarian cancer progression. We found that high expression of CYP27A1, the enzyme responsible for the synthesis of 27HC, was associated with decreased PFS, while high expression of CYP7B1, responsible for 27HC catabolism, was associated with increased PFS. However, 27HC decreased the cellular proliferation of various ovarian cancer cell lines in an LXR-dependent manner. Intriguingly, ID8 grafts were unable to effectively establish in CYP27A1-/- mice, indicating involvement of the host environment. Tumors from mice treated with 27HC had altered myeloid cell composition, and cells from the marrow stem cell lineage were found to be responsible for the effects in CYP27A1-/- mice. While inhibition of CYP27A1 or immune checkpoint did not significantly alter tumor size, their combination did, thereby highlighting this axis as a therapeutic target.

Bile Acid Homeostasis in a Cholesterol 7α-Hydroxylase and Sterol 27-Hydroxylase Double Knockout Mouse Model.

Bile acids (BAs) are diverse molecules that are synthesized from cholesterol in the liver. The synthesis of BAs has traditionally been shown to occur through two pathways. Cholesterol 7α-hydroxylase (CYP7A1) performs the initial and rate-limiting step in the classical pathway, and sterol 27-hydroxylase (CYP27A1) initiates the hydroxylation of cholesterol in the alternative pathway. While the role of individual BA species as physiological detergents is relatively ubiquitous, their endocrine functions as signaling molecules and roles in disease pathogenesis have been emerging to be BA species-specific. In order to better understand the pharmacologic and toxicologic roles of individual BA species in an in vivo model, we created cholesterol 7α-hydroxylase (Cyp7a1) and sterol 27-hydroxylase (Cyp27a1) double knockout (DKO) mice by cross-breeding single knockout mice (Cyp7a1-/- and Cyp27a1-/- ). BA profiling and quantification by liquid chromatography-mass spectrometry of serum, gallbladder, liver, small intestine, and colon of wild-type, Cyp7a1-/- , Cyp27a1-/- , and DKO mice showed that DKO mice exhibited a reduction of BAs in the plasma (45.9%), liver (60.2%), gallbladder (76.3%), small intestine (88.7%), and colon (93.6%), while maintaining a similar BA pool composition compared to wild-type mice. The function of the farnesoid X receptor (FXR) in DKO mice was lower, revealed by decreased mRNA expression of well-known FXR target genes, hepatic small heterodimer partner, and ileal fibroblast growth factor 15. However, response to FXR synthetic ligands was maintained in DKO mice as treatment with GW4064 resulted in similar changes in gene expression in all strains of mice. Conclusion: We provide a useful tool for studying the role of individual BAs in vivo; DKO mice have a significantly reduced BA pool, have a similar BA profile, and maintained response to FXR activation.

Vitamin D-Dependent Rickets Type 1B (25-Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?

Vitamin D requires a two-step activation by hydroxylation: The first step is catalyzed by hepatic 25-hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α-hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25-(OH)2 D. Mutations of CYP2R1 have been associated with vitamin D-dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss-of-function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss-of-function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25-OH-D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25-(OH)2 D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa-hydroxyvitamin D3 or alfacalcidol (1α-OH-D3 ) treatment, and we observed a dramatic increase in the 1,25-(OH)2 D serum concentration, which indicated the role of accessory 25-hydroxylase enzymes. Lastly, in patients who received calcifediol (25-OH-D3 ), we documented normal 24-hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25-OH-D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency. © 2017 American Society for Bone and Mineral Research.

Cholestenoic acid, an endogenous cholesterol metabolite, is a potent γ-secretase modulator.

BACKGROUND: Amyloid-ß (Aß) 42 has been implicated as the initiating molecule in the pathogenesis of Alzheimer's disease (AD); thus, therapeutic strategies that target Aß42 are of great interest. γ-Secretase modulators (GSMs) are small molecules that selectively decrease Aß42. We have previously reported that many acidic steroids are GSMs with potencies ranging in the low to mid micromolar concentration with 5ß-cholanic acid being the most potent steroid identified GSM with half maximal effective concentration (EC50) of 5.7 µM. RESULTS: We find that the endogenous cholesterol metabolite, 3ß-hydroxy-5-cholestenoic acid (CA), is a steroid GSM with enhanced potency (EC50 of 250 nM) relative to 5ß-cholanic acid. CA i) is found in human plasma at ~100-300 nM concentrations ii) has the typical acidic GSM signature of decreasing Aß42 and increasing Aß38 levels iii) is active in in vitro γ-secretase assay iv) is made in the brain. To test if CA acts as an endogenous GSM, we used Cyp27a1 knockout (Cyp27a1-/-) and Cyp7b1 knockout (Cyp7b1-/-) mice to investigate if manipulation of cholesterol metabolism pathways relevant to CA formation would affect brain Aß42 levels. Our data show that Cyp27a1-/- had increased brain Aß42, whereas Cyp7b1-/- mice had decreased brain Aß42 levels; however, peripheral dosing of up to 100 mg/kg CA did not affect brain Aß levels. Structure-activity relationship (SAR) studies with multiple known and novel CA analogs studies failed to reveal CA analogs with increased potency. CONCLUSION: These data suggest that CA may act as an endogenous GSM within the brain. Although it is conceptually attractive to try and increase the levels of CA in the brain for prevention of AD, our data suggest that this will not be easily accomplished.

27-hydroxycholesterol mediates negative effects of dietary cholesterol on cognition in mice.

In spite of the fact that cholesterol does not pass the blood-brain barrier, treatment of mice with dietary cholesterol causes significant effects on a number of genes in the brain and in addition a memory impairment. We have suggested that these effects are mediated by 27-hydroxycholesterol, which is able to pass the blood-brain barrier. To test this hypothesis we utilized Cyp27-/- mice lacking 27-hydroxycholesterol. The negative effect on memory observed after treatment of wildtype mice with dietary cholesterol was not observed in these mice. The cholesterol diet reduced the levels of the "memory protein" Arc (Activity Regulated Cytoskeleton associated protein) in the hippocampus of the wildtype mice but not in the hippocampus of the Cyp27-/- mice. The results are consistent with 27-hydroxycholesterol as the mediator of the negative effects of cholesterol on cognition.

Retinal and nonocular abnormalities in Cyp27a1(-/-)Cyp46a1(-/-) mice with dysfunctional metabolism of cholesterol.

Cholesterol elimination from nonhepatic cells involves metabolism to side-chain oxysterols, which serve as transport forms of cholesterol and bioactive molecules modulating a variety of cellular processes. Cholesterol metabolism is tissue specific, and its significance has not yet been established for the retina, where cytochromes P450 (CYP27A1 and CYP46A1) are the major cholesterol-metabolizing enzymes. We generated Cyp27a1(-/-)Cyp46a1(-/-) mice, which were lean and had normal serum cholesterol and glucose levels. These animals, however, had changes in the retinal vasculature, retina, and several nonocular organs (lungs, liver, and spleen). Changes in the retinal vasculature included structural abnormalities (retinal-choroidal anastomoses, arteriovenous shunts, increased permeability, dilation, nonperfusion, and capillary degeneration) and cholesterol deposition and oxidation in the vascular wall, which also exhibited increased adhesion of leukocytes and activation of the complement pathway. Changes in the retina included increased content of cholesterol and its metabolite, cholestanol, which were focally deposited at the apical and basal sides of the retinal pigment epithelium. Retinal macrophages of Cyp27a1(-/-)Cyp46a1(-/-) mice were activated, and oxidative stress was noted in their photoreceptor inner segments. Our findings demonstrate the importance of retinal cholesterol metabolism for maintenance of the normal retina, and suggest new targets for diseases affecting the retinal vasculature.

[Cerebrotendinous xanthomatosis: a multicentric retrospective study of 15 adults, clinical and paraclinical typical and atypical aspects]. / Étude rétrospective multicentrique de 15 cas adultes de xanthomatose cérébrotendineuse : aspects cliniques et paracliniques typiques et atypiques.

INTRODUCTION: Cerebrotendinous xanthomatosis, a metabolic leukodystrophy with an autosomal recessive inheritance, is secondary to deficiency of sterol 27-hydroxylase, an enzyme involved in cholesterol catabolism. Classical symptoms include clinical or infraclinical xanthomas affecting the skin and tendons, early cataracts, neurological signs and diarrhea. Brain imaging reveals involvement of the dentate nuclei and periventricular white matter hyperintensities. The diagnosis is based on an increased cholestanol level in serum, confirmed by the presence of a mutation in the CYP27A1 gene. Treatment is based on chenodeoxycholic acid. METHOD: We report a retrospective multicentric study of 15 cases of cerebrotendinous xanthomatosis diagnosed in French adults. Clinical, molecular and MRI findings were recorded in all patients. RESULTS: The average age at diagnosis was 39years (range 27-65). Disease onset occurred in childhood in 73% of patients and in adulthood in 27%. All patients with a pediatric onset were diagnosed during adulthood (age range 28-65years). Clinical symptoms variably associated cerebellar syndrome, pyramidal syndrome, cognitive decline, epilepsy, neuropathy (sought in 10 of our patients, present in forms in 8), psychiatric disorders, cataract and xanthomas. One patient had an atypical presentation: monoparesis associated with xanthomas. Brain MRI was abnormal in all: findings consisted in T2-weighted hyperintensity of the dentate nuclei (47%), periventricular leuoencephalopathy (73%) which preferentially involved the posterior cerebral part (60%), leucoencephalopathy with a vascular pattern (7%), hyperintensity of the cortico-spinal tracts (53%), globi pallidi, corpus callosum and cerebral atrophy (33%). Serum cholestanol was elevated in 93% of patients. The most frequent mutation was 1183C>T (n=5/15). Under treatment with chenodeoxycholic acid, eight patients improved initially, followed by stabilization in five of them, and worsening in the others. Four patients died. CONCLUSION: Patients with the xanthoma-neurological disorder association should be tested for cerebrotendinous xanthomatosis. The disease often begins in childhood with a diagnostic delay but also in adulthood. Involvement of the dentate nuclei is specific but not sensitive and the supratentorial leucoencephalopathy is not specific but with an antero-posterior gradient. A vascular distribution and involvement of the corpus callosum are possible. Serum cholestanol assay is very reliable: an elevated level provides the diagnosis, which must nevertheless be confirmed by molecular biology.

CYP2R1 is a major, but not exclusive, contributor to 25-hydroxyvitamin D production in vivo.

Bioactivation of vitamin D consists of two sequential hydroxylation steps to produce 1α,25-dihydroxyvitamin D3. It is clear that the second or 1α-hydroxylation step is carried out by a single enzyme, 25-hydroxyvitamin D 1α-hydroxylase CYP27B1. However, it is not certain what enzyme or enzymes are responsible for the initial 25-hydroxylation. An excellent case has been made for vitamin D 25-hydroxylase CYP2R1, but this hypothesis has not yet been tested. We have now produced Cyp2r1 (-/-) mice. These mice had greater than 50% reduction in serum 25-hydroxyvitamin D3. Curiously, the 1α,25-dihydroxyvitamin D3 level in the serum remained unchanged. These mice presented no health issues. A double knockout of Cyp2r1 and Cyp27a1 maintained a similar circulating level of 25-hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3. Our results support the idea that the CYP2R1 is the major enzyme responsible for 25-hydroxylation of vitamin D, but clearly a second, as-yet unknown, enzyme is another contributor to this important step in vitamin D activation.

The cholesterol derivative 27-hydroxycholesterol reduces steatohepatitis in mice.

BACKGROUND & AIMS: Non-alcoholic steatohepatitis is characterized by hepatic steatosis with inflammation. Although steatosis is benign and reversible, inflammation can increase liver damage. Hepatic inflammation has been associated with accumulation of cholesterol in lysosomes of Kupffer cells. 27-Hydroxycholesterol (27HC), a derivative of cholesterol formed by CYP27A1, can mobilize cholesterol from the lysosomes to the cytoplasm. We investigated whether 27HC can change the intracellular distribution cholesterol and reduce hepatic inflammation in mice. METHODS: We transplanted bone marrow from irradiated wild-type or Cyp27a1(-/-) mice to mice that do not express the low density lipoprotein receptor (Ldlr(-/-)), which are hyperlipidemic; 9 weeks later, mice were fed either regular chow or a high-fat, high-cholesterol (HFC) diet for 3 months. In a separate experiment, Ldlr(-/-) mice were given subcutaneous injections of 27HC and placed on regular chow or HFC diets for 3 weeks. Blood and liver tissues samples were collected and analyzed for intracellular cholesterol distribution and inflammation. RESULTS: In Ldlr(-/-) mice that received bone marrow transplants from Cyp27a1(-/-) mice, lysosomes of Kupfer cells had a greater accumulation of cholesterol than those of mice that received bone marrow from wild-type mice, after the HFC diet. Liver histology and gene expression analyses showed increased inflammation and liver damage in mice given bone marrow transplants from Cyp27a1(-/-) mice and placed on the HFC diet. Administration of 27HC to Ldlr(-/-) mice, following the HFC diet, reduced the accumulation of lysosomal cholesterol and hepatic inflammation, compared with mice that were not given 27HC. CONCLUSIONS: Accumulation of cholesterol in lysosomes of Kupfer cells promotes hepatic inflammation in mice. The cholesterol derivative 27HC reduces accumulation of cholesterol in lysosomes and might be used to treat non-alcoholic steatohepatitis.

Abnormal vascularization in mouse retina with dysregulated retinal cholesterol homeostasis.

Several lines of evidence suggest a link between age-related macular degeneration and retinal cholesterol maintenance. Cytochrome P450 27A1 (CYP27A1) is a ubiquitously expressed mitochondrial sterol 27-hydroxylase that plays an important role in the metabolism of cholesterol and cholesterol-related compounds. We conducted a comprehensive ophthalmic evaluation of mice lacking CYP27A1. We found that the loss of CYP27A1 led to dysregulation of retinal cholesterol homeostasis, including unexpected upregulation of retinal cholesterol biosynthesis. Cyp27a1-/- mice developed retinal lesions characterized by cholesterol deposition beneath the retinal pigment epithelium. Further, Cyp27a1-null mice showed pathological neovascularization, which likely arose from both the retina and the choroid, that led to the formation of retinal-choroidal anastomosis. Blood flow alterations and blood vessel leakage were noted in the areas of pathology. The Cyp27a1-/- retina was hypoxic and had activated Müller cells. We suggest a mechanism whereby abolished sterol 27-hydroxylase activity leads to vascular changes and identify Cyp27a1-/- mice as a model for one of the variants of type 3 retinal neovascularization occurring in some patients with age-related macular degeneration.

Four novel CYP27A1 mutations in seven Italian patients with CTX.

BACKGROUND AND PURPOSE: Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive disease, because of sterol 27-hydroxylase deficiency. Clinical manifestations of CTX are tendon xanthomas, juvenile cataracts, osteoporosis, diarrhoea and multiple progressive neurological dysfunctions. More than 300 patients with CTX have been reported to date worldwide and about fifty different mutations identified in CYP27A1 gene. This study describes the clinical and laboratory findings of seven new patients. METHODS: We report the molecular and clinical characterization of seven new Italian patients with CTX carrying four novel mutations. RESULTS: We identified four novel mutations located in different exons, in particular in the region of exons 2-5 of the CYP27A1 gene. Phenotypical expression did not differ from classical CTX presentation except for absence of tendon xanthomas in two patients.

Cerebrotendinous xanthomatosis (CTX): a treatable lipid storage disease.

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive lipid storage disease with multi-organ involvement. The clinical manifestations usually start at infancy and develop during the first and second decades of life; infantile-onset diarrhea may be the earliest clinical manifestation of CTX. Additional clinical manifestations are juvenile cataracts, tendon xanthomas, and multiple progressive neurological symptoms. Systemic manifestations that are often found include osteoporosis, heart involvement and premature arteriosclerosis. CTX is caused by mutations in the sterol 27 hydroxylase gene (CYP27) on chromosome 2q35-qter, which is responsible for conversion of cholesterol to cholic and chenodeoxycholic acid. Reduced synthesis of cholic and chenodeoxycholic acid results in failed feedback inhibition of cholesterol production, which in turn leads to increased serum cholestanol concentration and elevated urinary bile alcohols. Early treatment with chenodeoxycholic acid (CDCA) prevents the clinical symptoms and prevents deterioration. Although CTX is rare world wide, genetic islands of high frequency have been reported. In this review we would like to familiarize the reader with this fatal inborn error of metabolism that is possibly under-diagnosed and is preventable once recognized and treated.