The comparative toxicity of vitamin D metabolites in the weanling mouse

Impact of calcitriol and PGD2-G-loaded lipid nanocapsules on oligodendrocyte progenitor cell differentiation and remyelination

Multiple sclerosis (MS) is a demyelinating and inflammatory disease of the central nervous system (CNS) in need of a curative treatment. MS research has recently focused on the development of pro-remyelinating treatments and neuroprotective therapies. Here, we aimed at favoring remyelination and reducing neuro-inflammation in a cuprizone mouse model of brain demyelination using nanomedicines. We have selected lipid nanocapsules (LNC) coated with the cell-penetrating peptide transactivator of translation (TAT), loaded with either a pro-remyelinating compound, calcitriol (Cal-LNC TAT), or an anti-inflammatory bioactive lipid, prostaglandin D2-glycerol ester (PGD2-G) (PGD2-G-LNC TAT). Following the characterization of these formulations, we showed that Cal-LNC TAT in combination with PGD2-G-LNC TAT increased the mRNA expression of oligodendrocyte differentiation markers both in the CG-4 cell line and in primary mixed glial cell (MGC) cultures. However, while the combination of Cal-LNC TAT and PGD2-G-LNC TAT showed promising results in vitro, no significant impact, in terms of remyelination, astrogliosis, and microgliosis, was observed in vivo in the corpus callosum of cuprizone-treated mice following intranasal administration. Thus, although calcitriol's beneficial effects have been abundantly described in the literature in the context of MS, here, we show that the different doses of calcitriol tested had a negative impact on the mice well-being and showed no beneficial effect in the cuprizone model in terms of remyelination and neuro-inflammation, alone and when combined with PGD2-G-LNC TAT.

Impact of high-fat diet and vitamin D3 supplementation on aortic stenosis establishment in waved-2 epidermal growth factor receptor mutant mice

OBJECTIVE

The use of animal models of aortic stenosis (AS) remains essential to further elucidate its pathophysiology and to evaluate new therapeutic strategies. The waved-2 mouse AS model has been proposed; data have indicated that while aortic regurgitation (AR) is effectively induced, development of AS is rare. We aimed to evaluate the effect of high-fat diet (HFD) and vitamin D₃ supplementation in this model.

METHODS

HFD and subcutaneous vitamin D₃ injections were initiated at the age of 6 weeks until the age of 6 (n = 16, 6-month treatment group) and 9 (n = 11, 9-month treatment group) months. Twelve waved-2 mice without supplementation were used as control. Echocardiography was performed at 3, 6 and 9 months. Blood serum analysis (calcium, 1,25(OH)₂D₃ and cholesterol), histology and immunohistochemistry (CD-31, CD-68 and osteopontin) were evaluated at the end of the experiment (6 or 9 months).

RESULTS

Total cholesterol and 1,25(OH)₂D₃ were significantly increased relative to the control group. HFD and vitamin D₃ supplementation did result in improvements to the model, since AS was only detected in 6 (15.3%) mice (2 in the 3 groups) and AR was developed in the remaining animals. Echocardiographic parameters, fibrosis, thickness, inflammation and valvular calcification, were not significantly different between the 6-month treatment and control groups. Similar results were also observed in the 9-month treatment group.

CONCLUSION

These results suggest that HFD and vitamin D₃ supplementation have no effect in the waved-2 mouse model. This model essentially mimics AR and rarely AS. Further studies are needed to find a reliable animal model of AS.

Comparative therapeutic effects of orally administered 1,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(3) on type-1 diabetes in non-obese diabetic mice fed a normal-calcaemic diet

Frequent injections of the hormonal form of vitamin D(3), 1,25 dihydroxyvitamin D(3) (1,25D3) reportedly inhibits autoimmune type 1 diabetes (T1D) in non-obese diabetic (NOD) mice by correcting some of the abnormalities in antigen-presenting cells which contribute the development of pathogenic T cell responses. This route of administration greatly elevates the levels of these compounds in the bloodstream for hours after treatment, which requires mice to be fed diets formulated to contain much reduced levels of Ca to avoid the toxic effects of hypercalcaemia. In the current work, we demonstrate that feeding 1,25D3 or its synthetic precursor, 1alpha(OH) vitamin D(3) (1alphaD3), as part of a T1D supportive chow diet containing normal levels of Ca, is an effective means of reducing the incidence of disease in NOD mice, but the doses required for protection elicited hypercalcaemia. However, T1D protection elicited by D3 analogue feeding appears, at least partially, to have an immunological basis, as splenic T cells from treated mice had a decreased capacity to adoptively transfer disease. Protection is associated with an increased proportion of T cells with CD4+ forkhead box P3+ regulatory phenotype within the islet infiltrate of treated animals. The 1alphaD3 precursor is converted rapidly to the active 1,25D3 isoform in vivo. However, feeding the 1alphaD3 analogue elicited stronger T1D protection than the 1,25D3 compound, but also induced more severe hypercalcaemia. In future, the dietary supplementation of novel low-calcaemic D3 analogues may enable their continuous delivery at levels that inhibit T1D development in susceptible humans consuming normal levels of Ca.

Normal regulation of calcitriol production in Gy mice. Evidence for biochemical heterogeneity in the X-linked hypophosphatemic diseases

Phenotypic heterogeneity in X-linked hypophosphatemic rickets (XLH) is ascribed to variable penetrance of the genetic abnormality. However, studies of hypophosphatemic (Hyp) and gyrorotary (Gy) mice indicate that mutations at different loci along the X chromosome may underlie the genetically transmitted hypophosphatemic disorders. Thus, genetic heterogeneity may be a determinant of the phenotypic variability in XLH. To determine if such variance includes biochemical diversity, we examined whether Gy mice, similar to Hyp mice, exhibit abnormal regulation of renal 25-hydroxyvitamin D (25[OH]D)-1 alpha-hydroxylase. Serum phosphorus in Gy (4.7 +/- 0.3 mg/dl) and phosphate (P)-depleted mice (4.9 +/- 0.4) was significantly less than normal (8.4 +/- 0.5). Consistent with P depletion, the Gy mice exhibited enhanced renal 25(OH)D-1 alpha-hydroxylase activity (9.3 +/- 0.6 fmol/mg kidney per min), similar to that of P-depleted normals (9.1 +/- 1.5), but significantly greater than that of controls (3.1 +/- 0.3). Such normal enzyme responsiveness was confirmed upon PTH stimulation (1 IU/h s.c.), which revealed that Gy mice increased renal 1-hydroxylase (59 +/- 7.7) similarly to normals (65 +/- 7.7) and P-depleted animals (58.4 +/- 7.8). Calcitonin administration also enhanced enzyme function comparably in the animal models. Evidence confirming normally responsive calcitriol production in untreated Gy mice included increased serum 1,25-dihydroxyvitamin D levels, gastrointestinal calcium absorption, and urinary calcium. The normally regulated vitamin D metabolism in Gy mice indicates that biochemically diverse disease may result from mutations in the gene family regulating renal P transport and underlying X-linked hypophosphatemia. We suspect such heterogeneity is due to altered P transport at variable segments of the proximal convoluted tubule.