Synthesis and Biological Activity of 2,22-Dimethylene Analogues of 19-Norcalcitriol and Related Compounds.

Continuing our search for vitamin D analogues, we explored the modification of the steroidal side chain and inserted a methylene moiety in position C-22 together with either lengthening the side chain or introducing a ring at the terminal end. Our conformational studies confirmed that the presence of a methylene group attached to C-22 restricts the conformational flexibility of the side chain, which can result in changes in biological characteristics of a molecule. All synthesized 1α,25-dihydroxy-2,22-dimethylene-19-norvitamin D3 analogues proved equal to calcitriol in their ability to bind to the vitamin D receptor, and most of them exert significantly higher differentiation and transcriptional activity than calcitriol. The most active compounds were characterized by the presence of an elongated side chain or 26,27-dimethylene bridge. The synthetic strategy was based on the Wittig-Horner coupling of the known A-ring phosphine oxide with the corresponding Grundmann ketones prepared from a 20-epi-Inhoffen-Lythgoe diol derived from vitamin D2.

UV light suppression of EAE (a mouse model of multiple sclerosis) is independent of vitamin D and its receptor.

Vitamin D and sunlight have each been reported to protect against the development of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS). To date, the contribution of each has been unclear as ultra violet (UV) exposure also causes the generation of vitamin D in the skin. To examine whether the UV based suppression of EAE results, at least, in part from the production of vitamin D, we studied the effect of UV light on EAE in mice unable to produce 7-dehydroxycholesterol (7-DHC), the required precursor of vitamin D. Furthermore, we examined UV suppression of EAE in mice devoid of the vitamin D receptor (VDR). Our results demonstrate that UV light suppression of EAE occurs in the absence of vitamin D production and in the absence of VDR. Future investigations will focus on identifying the pathway responsible for the protective action of UV in EAE and presumably human MS.

Vitamin D deficiency in the ApcPirc/+ rat does not exacerbate colonic tumorigenesis, while low dietary calcium might be protective.

Human studies have shown that individuals with colon cancer tend to have lower serum 25-hydroxy-vitamin D3 [25(OH)D3] levels compared with healthy controls, but whether this link is causative, a result of the disease or an indicator of another factor altogether has yet to be demonstrated. In humans, vitamin D, calcium and UV exposure are inextricably linked; therefore, understanding the individual and combined roles of each of these will require animal models specifically designed to address these questions. To begin to untangle this network, our group has employed the ApcPirc/+ rat, which contains a truncating mutation in the Apc gene, leading to the development of colonic tumors. Our group previously utilized this model to demonstrate that vitamin D supplementation above normal does not reduce colonic tumor burden and, in fact, increased tumor multiplicity in a dose-dependent manner. In the current study, we tested whether vitamin D deficiency plays a causative role in tumor development using two strains which differ in their susceptibility to intestinal tumorigenesis. In the colon, vitamin D deficiency did not increase the development of tumors in either strain, and was actually protective in one strain. Unexpectedly, low dietary calcium combined with vitamin D deficiency significantly suppressed tumor development in the small intestine and colon of both strains. The vast majority of tumors in the human intestine occur in the colon, and we find no evidence to support a direct role of vitamin D deficiency in increasing colonic tumorigenesis, and low calcium might protect against tumor development.This article has an associated First Person interview with the first author of the paper.

2MD (DP001), a Single Agent in the Management of Hemodialysis Patients: A Randomized Trial.

BACKGROUND: Vitamin D analogs and calcimimetics are used to manage secondary hyperparathyroidism (SHPT) in dialysis patients. DP001 is an oral vitamin D analog that suppresses parathyroid hormone (PTH) in uremic rats, osteopenic women, and hemodialysis patients. The safety and effectiveness of DP001 suppressing PTH in dialysis patients previously managed with active vitamin D with or without a calcimimetic are presented. METHODS: A multicenter, randomized, double-blind study compared DP001 to placebo in hemodialysis patients with serum-intact PTH (iPTH) ≥300 pg/ml. The primary efficacy endpoint was the proportion of patients achieving 2 consecutive ≥30% decreases in iPTH levels during the 12 weeks of treatment. Calcium, phosphorus, calcium × phosphorus product and safety were also evaluated. The responses to DP001 were compared in patients previously treated with both active vitamin D and a calcimimetic to those previously on active vitamin D alone. RESULTS: Sixty-two patients were randomized (n = 34 DP001; n = 28 placebo). At week 12, 78% of all DP001-treated patients and 7% of all placebo-treated patients achieved the primary endpoint (p < 0.0001); iPTH fell 45% in the DP001 group and increased 37% in the placebo group. No patient exceeded the safety threshold of 2 consecutively corrected serum calcium levels ≥11.0 mg/dl. Patients previously on cinacalcet plus active vitamin D also responded to DP001 (n = 10) resulting in a 55% decrease in iPTH, while those on placebo (n = 9) increased by 70%. CONCLUSION: DP001 safely and effectively suppressed iPTH in hemodialysis patients with SHPT that were previously managed with active vitamin D alone or with a calcimimetic (www.clinicaltrials.gov, NCT01922843).

The association of mineral metabolism with vascular access patency.

BACKGROUND: Declining kidney function leads to progressively dysregulated mineral homeostasis and contributes to vascular calcification and a pro-inflammatory milieu, both of which play a critical role in loss of dialysis vascular access patency. We designed this study to examine the relationship between markers of bone and mineral metabolism, vitamin D replacement medications, and vascular access outcomes. We hypothesized that higher levels of calcium, phosphorous, parathyroid hormone (PTH), and albumin are independently associated with vascular access patency and that vitamin D supplementation is associated with lower risk of access failure. METHODOLOGY: We abstracted data on 204 consecutive patients referred for angiographic evaluation of their permanent arteriovenous access over a 25-month period. We followed patients from the time of access salvage until subsequent referral for access failure. RESULTS: The incidence of vascular access failure did not differ by serum phosphorus, PTH, calcium, calcium-phosphorus product or albumin level. Patients receiving any vitamin D replacement therapy, however, had a lower incidence of access failure compared to those receiving no therapy. Those receiving vitamin D3 therapy with or without paricalcitol (Zemplar, Abbot Laboratories, Abbot Park, IL) or calcitriol had an adjusted HR = 0.18 compared to those receiving no vitamin D therapy. CONCLUSIONS: This study suggests a relationship between vitamin D3 usage and better vascular access patency, independent of the effect of vitamin D on PTH. Though this relationship needs more rigorous investigation prior to clinical application, the known differences in the pro- and anti-inflammatory effects of various vitamin D metabolites provide a potential mechanism for these clinical observations.

Cholecalciferol or 25-hydroxycholecalciferol neither prevents nor treats adenomas in a rat model of familial colon cancer.

BACKGROUND: Epidemiologic studies in humans have shown associations between greater sunlight exposure, higher serum 25-hydroxycholecalciferol [25(OH)D3] concentrations, and reduced colon cancer risk. However, results from a limited number of vitamin D supplementation trials in humans have not shown a protective effect. OBJECTIVE: We sought to determine whether adding to the diet increasing amounts of either 25(OH)D3, the stable metabolite measured in serum and associated with cancer risk, or cholecalciferol (vitamin D3), the compound commonly used for supplementation in humans, could reduce emergent adenomas (chemoprevention) or decrease the growth of existing adenomas (treatment) in the colons of vitamin D-sufficient rats carrying a truncation mutation of adenomatous polyposis coli (Apc), a model of early intestinal cancer. METHODS: Apc(Pirc/+) rats were supplemented with either vitamin D3 over a range of 4 doses [6-1500 µg/(kg body weight · d)] or with 25(OH)D3 over a range of 6 doses [60-4500 µg/(kg body weight · d)] beginning after weaning. Rats underwent colonoscopy every other week to assess effects on adenoma number and size. At termination (140 d of age), the number of tumors in the small intestine and colon and the size of tumors in the colon were determined, and serum calcium and 25(OH)D3 measurements were obtained. RESULTS: At lower doses (those that did not affect body weight), neither of the vitamin D compounds reduced the number of existing or emergent colonic tumors (P-trend > 0.24). By contrast, supplementation at higher doses (those that caused a suppression in body weight gain) with either 25(OH)D3 or vitamin D3 caused a dose-dependent increase in colonic tumor number in both males and females (P-trend < 0.003). CONCLUSIONS: No evidence for protection against colon tumor development was seen with lower dose supplementation with either cholecalciferol or 25-hydroxycholecalciferol. Thus, the association between sunlight exposure and the incidence of colon cancer may involve factors other than vitamin D concentrations. Alternative hypotheses warrant investigation. Furthermore, this study provides preliminary evidence for the need for caution regarding vitamin D supplementation of humans at higher doses, especially in individuals with sufficient serum 25(OH)D3 concentrations.

Synthesis and Biological Activity of 25-Hydroxy-2-methylene-vitamin D3 analogues monohydroxylated in the A-ring.

The 20R- and 20S-isomers of 25-hydroxy-2-methylene-vitamin D3 and 3-desoxy-1α,25-dihydroxy-2-methylene-vitamin D3 have been synthesized. Two alternative synthetic routes were devised for preparation of the required A-ring synthons, starting from the chiral compound derived from the (-)-quinic acid and, alternatively, from the commercially available achiral precursor, monoprotected 1,4-cyclohexanedione. The A-ring dienynes were coupled by the Sonogashira process with the respective C,D-ring fragments, the enol triflates derived from the protected (20R)- or (20S)-25-hydroxy Grundmann ketones. All four compounds possessed significant in vivo activity on bone calcium mobilization and intestinal calcium transport. The presence of a 2-methylene group increased intestinal calcium transport activity of all four analogues above that of the native hormone, 1α,25-dihydroxyvitamin D3. In contrast, bone calcium mobilization was equal to that produced by 1α,25-dihydroxyvitamin D3 in compounds having a (20S)-configuration or diminished to one-tenth that of 1α,25-dihydroxyvitamin D3 in compounds with a (20R)-configuration.

Novel, selective vitamin D analog suppresses parathyroid hormone in uremic animals and postmenopausal women.

BACKGROUND: The use of 1α-hydroxylated vitamin D therapy to control secondary hyperparathyroidism in renal failure patients has been a success story, culminating with the demonstration of increased life expectancy in patients treated with these compounds. However, hypercalcemic episodes have been a recurrent problem with these therapies and have resulted in the added use of calcium mimetics. Clearly there is good reason to search for improved vitamin D therapy. In our inventory of vitamin D compounds, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D3 (2MD) surfaced as a potential candidate. This was based on its preferential localization in the parathyroid gland and a clear suppression of serum parathyroid hormone (PTH) levels without a change in serum calcium in a clinical trial in postmenopausal women. METHODS: 2MD has now been tested in the rat 5/6-nephrectomy model of renal failure, and in postmenopausal women to determine if it can suppress serum PTH at doses that do not elevate serum calcium and serum phosphorus concentrations. RESULTS: Daily oral treatment of uremic rats on 2.5 ng/bw/day of 2MD dramatically suppressed PTH without a change in serum calcium or serum phosphorus. Further, PTH was suppressed in postmenopausal women after only 3 daily oral doses of 2MD that continued for 4 weeks with no change in serum calcium or serum phosphorus. CONCLUSION: These results coupled with a pharmacokinetic half-life of ~24 h suggest that 2MD given either daily or at the time of dialysis may be a superior therapy for secondary hyperparathyroidism in chronic renal failure patients.

Clinical utility of simultaneous quantitation of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D by LC-MS/MS involving derivatization with DMEQ-TAD.

CONTEXT: The discovery of hypercalcemic diseases due to loss-of-function mutations in 25-hydroxyvitamin D-24-hydroxylase has placed a new demand for sensitive and precise assays for 24,25-dihydroxyvitamin D [24,25-(OH)2D]. OBJECTIVE: We describe a novel liquid chromatography and tandem mass spectrometry-based method involving derivatization with DMEQ-TAD {4-[2-(6,7-dimethoxy-4-methyl-3,4-dihydroquinoxalinyl)ethyl]-1,2,4-triazoline-3,5-dione} to simultaneously assay multiple vitamin D metabolites including 25-hydroxyvitamin D (25-OH-D) and 24,25-(OH)2D using 100 µL of serum with a 5-minute run time. DESIGN: The assay uses a newly synthesized internal standard d6-24,25-(OH)2D3 enabling the quantitation of 24,25-(OH)2D3 as well as the determination of the ratio of 25-OH-D3 to 24,25-(OH)2D3, a physiologically useful parameter. SETTING: We report data on more than 1000 normal and disease samples involving vitamin D deficiency or hypercalcemia in addition to studies involving knockout mouse models. RESULTS: The assay showed good correlation with samples from quality assurance schemes for 25-OH-D (25-OH-D2 and 25-OH-D3) determination (-2% to -5% bias) and exhibited low inter- and intraassay coefficients of variation (4%-7%) and lower limits of quantitation of 0.25-0.45 nmol/L. In clinical studies, we found a strong correlation between serum levels of 25-OH-D3 and 24,25-(OH)2D3 (r(2) = 0.80) in subjects over a broad range of 25-OH-D3 values and a marked lack of production of 24,25-(OH)2D3 below 25 nmol/L of 25-OH-D. The ratio of 25-OH-D3 to 24,25-(OH)2D3, which remained less than 25 in vitamin D-sufficient subjects (serum 25-OH-D < 50 nmol/L) but was greatly elevated (80-100) in patients with idiopathic infantile hypercalcemia. CONCLUSIONS: The new method showed good utility in clinical settings involving vitamin D deficiency; supplementation with vitamin D and idiopathic infantile hypercalcemia, as well as in animal models with ablation of selected cytochrome P450-containing enzymes involved in vitamin D metabolism.

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.

Synthesis and biological activity of 25-hydroxy-2-methylene-vitamin D3 compounds.

We have recently obtained 1-desoxy and 3-desoxy analogs of (20S)-1α,25-dihydroxy-2-methylene-19-norvitamin D3 (2MD), a compound exerting significantly enhanced calcemic activity and currently being evaluated as a potential drug for osteoporosis. In order to further explore this class of pharmacologically important vitamin D compounds we have decided to synthesize analogs characterized by the presence of two A-ring exocyclic methylene groups attached to C-2 and C-10. The Sonogashira coupling of a triflate enol of the protected (20R)- or (20S)-25-hydroxy Grundmann ketone and the corresponding dienyne A-ring fragment provided the target compounds. A new synthetic path was elaborated, leading to the desired A-ring synthon, that started from commercially available 1,4-cyclohexanedione monoethylene acetal. Biological in vitro and in vivo activities of the synthesized 25-hydroxy-2-methylene-vitamin D3 compounds, belonging to 20R- and 20S-series, were evaluated and discussed. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Synthesis and biological evaluation of novel 6-substituted analogs of 1α,25-dihydroxy-19-norvitamin D3.

We have recently described the synthesis and biological evaluation of 1α,25-dihydroxy-6-methylvitamin D3 which binds the vitamin D receptor (VDR) very effectively. Unfortunately, this compound has a strong tendency to rearrange to its previtamin form. Taking this into consideration, we decided to synthesize a series of 6-substituted analogs of 1α,25-dihydroxy-19-norvitamin D3 which lack the exomethylene moiety at C-10 and thus are unable to undergo a conversion to their respective previtamin forms. The synthesis of analogs bearing different substituents at C-6 was accomplished by Suzuki-Miyaura cross-coupling reaction of a bicyclic organoboron derivative (CD-ring fragment) with the respective alkenyl halides (A-ring synthons). The biological in vitro studies of the affinity of synthesized analogs to the full-length recombinant rat VDR indicate that presence of a bulky, polar substituent at C-6 results in decrease in binding ability. Moreover, introduction of a 6-methyl substituent into the 1α,25-dihydroxy-19-norvitamin D3 molecule results in the 9 times lower affinity of the homolog to the VDR while the same modification of calcitriol has not influenced binding activity. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Ring-A-seco analogs of 1α,25-dihydroxy-19-norvitamin D3.

The steroid hormone 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2D3] is the most active metabolite of vitamin D3 which exerts its control over a multitude of biological processes related to calcium and phosphorus homeostasis, cell proliferation and differentiation, and immune regulation. Unfortunately, the therapeutic application of 1α,25-(OH)2D3 is limited by induction of hypercalcemia. The need for vitamin D compounds with selective biological profiles has stimulated the synthesis of more than three thousand analogs of 1α,25-(OH)2D3. Most of these compounds have structural modifications in the side chain and A-ring; there is also an increasing number of modifications in the CD-rings and limited number in the triene system (seco-B ring). Herein, we report the synthesis and biological evaluation of seco-A-19-nor analogs of 1α,25-dihydroxyvitamin D3, developed to study the role of ring A in the biological activity of 1α,25-(OH)2D3. Interestingly, compounds 2 and 4 show substantial ability to bind the vitamin D receptor and the former is also characterized by selective intestinal calcium transport activity. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Synthesis of novel 19-norvitamin D3 analogs with unnatural triene system.

9-Alkylidene analogs of 19-nor-1α,25-(OH)2D3 were synthesized, possessing a 'reversed' triene system compared to the natural hormone. The conjugated triene moiety of the novel analogs was constructed by coupling an enyne anion, representing an A-ring synthon, with a 9α-substituted Grundmann ketone derivative. Regioselective dehydration followed by semihydrogenation under Lindlar conditions, provided the desired 9-alkylated 19-norprevitamins which were thermally isomerized to the corresponding 9-methylene and 9-ethylidene analogs of 19-norcalcitriol. It was established that only the former compound had significant binding affinity to the full-length recombinant rat vitamin D receptor. The remaining in vitro studies show very low activity of both analogs. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Supplementation by vitamin D compounds does not affect colonic tumor development in vitamin D sufficient murine models.

Epidemiological studies indicate that sunlight exposure and vitamin D are each associated with a lower risk of colon cancer. The few controlled supplementation trials testing vitamin D in humans reported to date show conflicting results. We have used two genetic models of familial colon cancer, the Apc(Pirc/+) (Pirc) rat and the Apc(Min/+) (Min) mouse, to investigate the effect of 25-hydroxyvitamin D(3) [25(OH)D(3)] and two analogs of vitamin D hormone on colonic tumors. Longitudinal endoscopic monitoring allowed us to test the efficacy of these compounds in preventing newly arising colonic tumors and in affecting established colonic tumors. 25(OH)D(3) and two analogs of vitamin D hormone each failed to reduce tumor multiplicities or alter the growth patterns of colonic tumors in the Pirc rat or the Min mouse.

Screening of selective inhibitors of 1α,25-dihydroxyvitamin D3 24-hydroxylase using recombinant human enzyme expressed in Escherichia coli.

High-level heterologous expression of human 1α,25-dihydroxyvitamin D(3) 24-hydroxylase (CYP24A1) in Escherichia coli was attained via a fusion construct by appending the mature CYP24A1 without the leader sequence to the maltose binding protein (MBP). Facile purification was achieved efficiently through affinity chromatography and afforded fully functional enzyme of near homogeneity, with a k(cat) of 0.12 min(-1) and a K(M) of 0.19 µM toward 1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. A convenient and reliable cell-free assay was established and used to screen vitamin D analogues with potential inhibitory properties toward CYP24A1. Some of the compounds exhibited potent inhibition with K(I) values as low as 0.021 µM. Furthermore, TS17 and CPA1 exhibited superior specificity toward CYP24A1 over 25-hydroxyvitamin D(3) 1α-hydroxylase (CYP27B1), with selectivities of 39 and 80, respectively. Addition of TS17 or CPA1 to a mouse osteoblast culture sustained the level of 1,25(OH)(2)D(3) in the medium. Their activities in vitamin D receptor (VDR) binding, CYP24A1 transcription, and HL-60 cell differentiation were evaluated as well.

1-desoxy analog of 2MD: synthesis and biological activity of (20S)-25-hydroxy-2-methylene-19-norvitamin D3.

During our ongoing structure-activity studies in the vitamin D area, we obtained (20S)-1alpha,25-dihydroxy-2-methylene-19-norvitamin D3 (5). This analog, designated 2MD, is characterized by a significantly enhanced calcemic activity and is currently evaluated as a potential drug for osteoporosis. Therefore, it was of interest to synthesize also its 1-desoxy analog and to evaluate its biological action. These studies were aimed at solving an intriguing problem: can such a vitamin also be hydroxylated in vivo at the allylic C-1 position despite lack of the exomethylene moiety at C-10? The Wittig-Horner coupling of the known protected (20S)-25-hydroxy Grundmann ketone 17 and the phosphine oxides 16 and 33, differing in their hydroxyls protection, provided the target 1-desoxy-2MD (6) after removal of the silyl protecting groups. Two synthetic paths have been elaborated leading to the desired A-ring synthons and starting from commercially available compounds: 1,4-cyclohexanedione monoethylene acetal (7) and (-)-quinic acid (19). The biological activity in vitro of the synthesized 1-desoxy-2MD (6) was evaluated and this analog was found to have an affinity for the vitamin D receptor (VDR) similar as its parent compound 2MD (5) while being much less active in the transcriptional assay. The results of the biological tests in vivo are also discussed.

UV radiation suppresses experimental autoimmune encephalomyelitis independent of vitamin D production.

Although the exact cause of multiple sclerosis (MS) is unknown, a number of genetic and environmental factors are thought to influence MS susceptibility. One potential environmental factor is sunlight and the subsequent production of vitamin D. A number of studies have correlated decreased exposure to UV radiation (UVR) and low serum 25-hydroxyvitamin D(3) [25(OH)D(3)] levels with an increased risk for developing MS. Furthermore, both UVR and the active form of vitamin D, 1alpha,25-dihydroxyvitamin D(3), suppress disease in the experimental autoimmune encephalomyelitis (EAE) animal model of MS. These observations led to the hypothesis that UVR likely suppresses disease through the increased production of vitamin D. However, UVR can suppress the immune system independent of vitamin D. Therefore, it is unclear whether UVR, vitamin D, or both are necessary for the putative decrease in MS susceptibility. We have probed the ability of UVR to suppress disease in the EAE model of MS and assessed the effect of UVR on serum 25(OH)D(3) and calcium levels. Our results indicate that continuous treatment with UVR dramatically suppresses clinical signs of EAE. Interestingly, disease suppression occurs with only a modest, transient increase in serum 25(OH)D(3) levels. Further analysis demonstrated that the levels of 25(OH)D(3) obtained upon UVR treatment were insufficient to suppress EAE independent of UVR treatment. These results suggest that UVR is likely suppressing disease independent of vitamin D production, and that vitamin D supplementation alone may not replace the ability of sunlight to reduce MS susceptibility.

Vitamin D and the parenteral nutrition patient.

Vitamin D is a prohormone produced in the skin epidermis when irradiated with sunlight or ultraviolet light B. It is also absorbed from food or supplements. Vitamin D must be converted to 25-hydroxyvitamin D3 (circulating form) and finally to the hormone, 1a,25-dihydroxyvitamin D3, before it can function. This hormone acts through a single nuclear receptor. The details of these conversions and molecular biology of the action of vitamin D3 are summarized. The physiologic functions of vitamin D have been expanded beyond the mineralization of the skeleton to include modulation of the immune system, terminal differentiation in several tissues, suppression of malignant cells, and anabolic activity in the skeleton and in the renal-cardiovascular system. Epidemiologic studies have associated vitamin D deficiency with an increased risk of colorectal and breast cancers and an increased risk of autoimmune diseases, such as multiple sclerosis, type 1 diabetes, and cardiovascular events. Thus, vitamin D is essential not only for the skeleton but also many other organ systems. Recommendations for 25-hydroxyvitamin D3 levels for PN patients are presented.

Diaminobutane (DAB) dendrimers are potent binders of oral phosphate.

Reduction of blood phosphorus is a critical component in the management of secondary hyperparathyroidism in chronic kidney disease patients. In addition to dialysis treatment and dietary phosphorus restriction, oral phosphate binders are often consumed with meals to reduce the availability of food phosphorus. Several oral phosphate binders are approved for use in chronic kidney disease patients, but all have practical limitations because of toxicity, poor efficacy, or high cost. Using an in vivo method to measure intestinal phosphate absorption in rats using radiolabeled phosphate, we found that first-, second-, third-, and fifth-generation diaminobutane dendrimer compounds, DAB-4-Cl, DAB-8-Cl, DAB-16-Cl, and DAB-64-Cl, respectively, drastically reduce the absorption of inorganic phosphate in a dose-dependent manner. To avoid complications of metabolic acidosis caused by hydrochloride salts, an acetate salt, DAB-9-AcOH, was prepared and shown to be equally effective at binding radiolabeled phosphate as DAB-8-Cl. DAB-8-AcOH was further shown to increase fecal phosphorus and decrease serum phosphorus in a dose-dependent manner when fed to rats. These data suggest that dendrimer compounds are of great potential use in the binding of food phosphate for the management of hyperparathyroidism secondary to chronic kidney disease.