Vitamin D receptor amounts across different segments of the gastrointestinal tract in Brown Swiss and Holstein Frisean cows of different age

Periparturient Mineral Metabolism: Implications to Health and Productivity

Mineral metabolism, in particular Ca, and to a lesser extent phosphorus (P) and magnesium (Mg), is altered with the onset of lactation because of extensive irreversible loss to synthesize colostrum and milk. The transient reduction in the concentration of Ca in blood, particularly when it lasts days, increases the risk of mineral-related disorders such as hypocalcemia and, to a lesser extent, hypophosphatemia. Although the incidence of clinical hypocalcemia can be reduced by prepartum dietary interventions, subclinical hypocalcemia remains prevalent, affecting up to 60% of the dairy cows in the first 3 d postpartum. More importantly, strong associations exist between hypocalcemia and increased susceptibility to other peripartum diseases and impaired reproductive performance. Mechanistic experiments have demonstrated the role of Ca on innate immune response in dairy cows, which presumably predisposes them to other diseases. Hypocalcemia is not related to inadequate Ca intake as prepartum diets marginal to deficient in Ca reduce the risk of the disease. Therefore, the understanding of how Ca homeostasis is regulated, in particular how calciotropic hormones such as parathyroid hormone and 1,25-dihydroxyvitamin D3, affect blood Ca concentrations, gastrointestinal Ca absorption, bone remodeling, and renal excretion of Ca become critical to develop novel strategies to prevent mineral imbalances either by nutritional or pharmacological interventions. A common method to reduce the risk of hypocalcemia is the manipulation of the prepartum dietary cation-anion difference. Feeding acidogenic diets not only improves Ca homeostasis and reduces hypocalcemia, but also reduces the risk of uterine diseases and improves productive performance. Feeding diets that induce a negative Ca balance in the last weeks of gestation also reduce the risk of clinical hypocalcemia, and recent work shows that the incorporation of mineral sequestering agents, presumably by reducing the absorption of P and Ca prepartum, increases blood Ca at calving, although benefits to production and health remain to be shown. Alternative strategies to minimize subclinical hypocalcemia with the use of vitamin D metabolites either fed prepartum or as a pharmacological agent administered immediately after calving have shown promising results in reducing hypocalcemia and altering immune cell function, which might prove efficacious to prevent diseases in early lactation. This review summarizes the current understanding of Ca homeostasis around parturition, the limited knowledge of the exact mechanisms for gastrointestinal Ca absorption in bovine, the implications of hypocalcemia on the health of dairy cows, and discusses the methods to minimize the risk of hypocalcemia and their impacts on productive performance and health in dairy cows.

Rabbits (Oryctolagus cuniculus) increase caecal calcium absorption at increasing dietary calcium levels

Hindgut fermenting herbivores from different vertebrate taxa, including tortoises, and among mammals some afrotheria, perissodactyla incl. equids, several rodents as well as lagomorphs absorb more calcium (Ca) from the digesta than they require, and excrete the surplus via urine. Both proximate and ultimate causes are elusive. It was suggested that this mechanism might ensure phosphorus availability for the hindgut microbiome by removing potentially complex-building Ca from the digesta. Here we use Ussing chamber experiments to show that rabbits (Oryctolagus cuniculus) maintained on four different diets (six animals/diet) increase active Ca absorption at increasing Ca levels. This contradicts the common assumption that at higher dietary levels, where passive uptake should be more prevalent, active transport can relax and hence supports the deliberate removal hypothesis. In the rabbits, this absorption was distinctively higher in the caecum than in the duodenum, which is unexpected in mammals. Additional quantification of the presence of two proteins involved in active Ca absorption (calbindin-D9K CB; vitamin D receptor, VDR) showed higher presence with higher dietary Ca. However, their detailed distribution across the intestinal tract and the diet groups suggests that other factors not investigated in this study must play major roles in Ca absorption in rabbits. Investigating strategies of herbivores to mitigate potential negative effects of Ca in the digesta on microbial activity and growth might represent a promising area of future research.

Blood calcium concentration and performance in periparturient and early lactating dairy cows is influenced by plant bioactive lipid compounds

Previous studies ex vivo suggested that plant bioactive lipid compounds (PBLC) can increase ruminal calcium absorption. Therefore, we hypothesized that PBLC feeding around calving may potentially counteract hypocalcemia and support performance in postpartum dairy cows. The corresponding aim of the study was to investigate the effect of PBLC feeding on blood minerals in Brown Swiss (BS) and hypocalcemia-susceptible Holstein Friesian (HF) cows during the period from d -2 to 28 relative to calving and on milk performance until d 80 of lactation. A total of 29 BS cows and 41 HF cows were divided each into a control (CON) and PBLC treatment group. The latter was supplemented with 1.7 g/d menthol-rich PBLC from 8 d before expected calving to 80 d postpartum. Milk yield and composition, body condition score and blood minerals were measured. Feeding PBLC induced a significant breed × treatment interaction for iCa, supporting that PBLC increased iCa exclusively in HF cows; the increase was 0.03 mM over the whole period and 0.05 mM from d 1 to 3 after calving. Subclinical hypocalcemia was seen in one BS-CON and 8 HF-CON cows and 2 BS-PBLC and 4 HF-PBLC cows. Clinical milk fever was detected only in HF cows (2 HF-CON and one HF-PBLC). Other tested blood minerals, such as sodium, chloride, and potassium, as well as blood glucose, were neither affected by PBLC feeding nor breed, nor were their 2-way interactions, except for higher sodium levels in PBLC cows on d 21. Body condition score showed no effect of treatment, except for a lower body condition score in BS-PBLC compared with BS-CON at d 14. Dietary PBLC increased milk yield, milk fat yield, and milk protein yield at 2 consecutive dairy herd improvement test days. As indicated by treatment × day interactions, energy-corrected milk yield and milk lactose yield were increased by PBLC on the first test day only, and milk protein concentration decreased from test d 1 to test d 2 in CON only. The concentrations of fat, lactose, and urea, as well as somatic cell count, were not affected by treatment. The weekly milk yield over the first 11 wk of lactation was 29.5 kg/wk higher for PBLC versus CON across breeds. It is concluded that the applied PBLC induced a small but measurable improvement of calcium status in HF cows in the study period and had additional positive effects on milk performance in both breeds.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D₃ or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for β-amyloid peptide efflux and influx, the sodium phosphate transporters (NaP_i), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTβ) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aβ) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Patterns of calcium channel (TRPV6) expression in rabbit gut epithelium

<p>The present study was undertaken to explore the immunohistochemical localisation of TRPV6 calcium channels in rabbit gut epithelium that are actively involved in calcium absorption. To undertake the research, twelve apparently healthy adult female rabbits with a body weight between 1.0 to 1.5 kg were procured, acclimatised and divided into two groups: control and test. Both groups were kept on same feed along with exogenous calcium supplementation in test group animals only. The serum calcium level revealed that normally a high value of serum calcium is maintained in the rabbit as compared to other mammals, thus indicating that the homeostatic mechanism might be poorly developed. Immunohistochemistry and reverse transcription polymerase chain reaction analysis revealed that the caecum was the site of maximum calcium absorption in rabbit, followed by the duodenum and jejunum. The expression pattern of TRPV6 protein/mRNA was weaker in test group animals than in the control group, indicating that the channel was functional in low calcium concentration in the gut.</p>

Influence of feeding and UVB exposition on the absorption mechanisms of calcium in the gastrointestinal tract of veiled chameleons (Chamaeleo calyptratus)

The purpose of this study was to investigate the influence of feeding and UVB exposition on the occurrence and distribution patterns of vitamin D receptors (VDR) and calbindin D28k (Cb-D28k) in the gastrointestinal tract of veiled chameleons. Thus, 56 veiled chameleon hatchlings were divided into six treatment groups: UV (with UVB exposure); No (no supplements, no UVB exposure); CaAUV (with calcium (Ca), vitamin A supplementation, UVB exposure); CaA (with Ca, vitamin A supplementation); CaADUV (with Ca, vitamin A, vitamin D supplementation, UVB exposure); and CaAD (with Ca, vitamin A, vitamin D supplementation). Animals were reared under the suspected conditions for 6 months on locust-based diets. Tissue samples of stomach, duodenum, ileum and colon were taken, and semi-quantitative immunohistochemical methods (IHC) were performed to detect Cb-D28k and VDR. VDR immunoreactions were higher in the luminal epithelium of the duodenum than in that of the ileum. VDR immunoreactions in the luminal epithelium were higher at the base of the villi of the duodenum as compared to the tip. Cb-D28k immunoreactions were mainly observed in the luminal epithelium of the duodenum. The two groups treated with all dietary supplements (CaADUV, CaAD) exhibited a higher Cb-D28k immunoreaction as those with no supplements and UVB exposure only. No immunoreaction for both proteins could be detected in the stomach. This study suggests that the duodenum plays an important role in the active transcellular absorption of Ca in veiled chameleons as shown by the immunohistochemical detection of VDR and Cb-D28k. Expression of Cb-D28k, in particular, appears to be regulated by dietary supplementation of vitamin D and vitamin A. VDRs, however, tended to be upregulated when animals were not supplemented with Ca, vitamin D and vitamin A. This may be due to the decreased Ca concentrations which caused vitamin D activation in the skin without any supplementation, but UVB exposure.

Immunohistochemistry of deparaffinised sections using antigen retrieval with microwave combined pressure cooking versus immunofluorescence in the assessment of human renal biopsies

BACKGROUND

Immunofluorescence of frozen tissue sections (IF-F) is a traditional technique used in renal biopsy. However, IF-F has certain disadvantages, such as a few or even no glomeruli in the section, and limited long-term preservation of the fluorescently labelled samples.

METHODS

We compared two-step immunohistochemistry (IHC) staining of deparaffinised sections for antigen retrieval with microwave combined high-pressure cooking to IF-F used to detect antigens of IgG, IgA, IgM, C3, C1q, κ and λ in patient renal biopsy samples. The number of glomeruli detected, sensitivity and specificity of positive staining, tissue structure, and location staining of the antigens were determined using the two methods in 285 patients diagnosed with different renal diseases.

RESULTS

Concordant observations between IF-F and IHC were 99% for all antigen staining (1969 of 1995 observations) and 100% for IgG, IgA and IgM (all 285 observations). The number of glomeruli in IHC sections was significantly greater compared with IF-F sections (p<0.001). IHC provided clearer images of tissue structure, more precise localisation of positive-staining antigens, and IHC staining allowed simultaneous evaluation of tissue by light microscopy. Correlation between tissue structure and immune deposits are not readily attained by IF-F.

CONCLUSIONS

IHC is superior to IF-F for immunopathological diagnosis of renal biopsy tissue and is a reliable replacement for the more traditional IF-F method.

Immunofluorescence with dual microwave retrieval of paraffin-embedded sections in the assessment of human renal biopsy specimens

Immunofluorescence of frozen tissue sections (IF-F) is a classic technique for renal immunopathologic examination. However, it has certain disadvantages, such as diffuse antigen distribution and few or even no glomeruli in the section. We developed a new technique of immunofluorescence staining using dual microwave retrieval in paraffin-embedded renal tissue sections (IF-DMP) and compared IF-DMP with IF-F in 406 renal biopsy samples. IF-DMP detected significantly more glomeruli than did IF-F (P< .001). There was no significant difference for the specificity and sensitivity in the detection of immunoglobulins, complements, κ, and λ between IF-F and IF-DMP. Concordant observations were 98% for all immunofluorescence, complements, κ, and λ staining and 100% for immunoglobulin staining. Both techniques were completely accurate in confirming diagnoses of various glomerular diseases. IF-DMP provided clearer images of tissue structure and more precise localization of antigens, and it is a suitable alternative for traditional IF-F in clinical renal immunopathologic diagnosis.

Allelic variations in coding regions of the vitamin D receptor gene in dairy cows and potential susceptibility to periparturient hypocalcaemia

Periparturient hypocalcaemia (milk fever) is a disorder of Ca metabolism in dairy cattle primarily affecting multiparous cows. The major reasons for the rapid decrease of blood Ca concentration after calving are the prompt increase of Ca secretion into the colostrum and the delayed activation of Ca regulation mechanisms including calcitriol, a metabolite of vitamin D. In man, vitamin D receptor (VDR) gene polymorphisms are reported to be associated with disturbances of Ca metabolism, whereas data confirming the same in dairy cows are still missing. Moreover, polymorphisms that only affect non-coding regions are sometimes difficult to ascribe to a specific disorder as pathways and unequivocal links remain elusive. Therefore, the idea of the present study was to investigate in a small group of dairy cows with documented clinical records whether polymorphisms in the coding regions of the VDR gene existed and whether these potentially found variations were correlated with the incidence of periparturient hypocalcaemia. For this purpose, blood DNA was isolated from 26 dairy cows in their 4th to 6th lactation, out of which 17 had experienced hypocalcaemia at least once, whereas 9 cows had never undergone periparturient hypocalcaemia in their lifetime. The 10 VDR exons and small parts of adjacent introns were sequenced and compared with the Bos taurus VDR sequence published on NCBI based on the DNA of one Hereford cow. In total, 8 sequence alterations were detected in the fragments, which were primarily heterozygous. However, only 4 of them were really located on exons thereby potentially causing changes of the encoded amino acid of the VDR protein, but were not correlated with the incidence of periparturient hypocalcaemia. Certainly, this lack of statistical correlation could be due to the small number of animals included; anyhow, it was not encouraging enough to initiate a larger study with hundreds of cows and document blood Ca levels post partum for at least four lactations.

A novel model to explain dietary factors affecting hypocalcaemia in dairy cattle

Most dairy cows exhibit different degrees of hypocalcaemia around calving because the gestational Ca requirements shift to the disproportionately high Ca requirements of lactation. Ca homeostasis is a robust system that effectively adapts to changes in Ca demand or supply. However, these adaptations often are not rapid enough to avoid hypocalcaemia. A delay in the reconfiguration of intestinal Ca absorption and bone resorption is probably the underlying cause of this transient hypocalcaemia. Several dietary factors that affect different aspects of Ca metabolism are known to reduce the incidence of milk fever. The present review describes the interactions between nutrition and Ca homeostasis using observations from cattle and extrapolations from other species and aims to quantitatively model the effects of the nutritional approaches that are used to induce dry cows into an early adaptation of Ca metabolism. The present model suggests that reducing dietary cation–anion difference (DCAD) increases Ca clearance from the blood by dietary induction of systemic acidosis, which results in hypercalciuria due to the loss of function of the renal Ca transient receptor potential vanilloid channel TRPV5. Alternatively, reducing the gastrointestinal availability of Ca by reducing dietary Ca or its nutritional availability will also induce the activation of Ca metabolism to compensate for basal blood Ca clearance. Our model of gastrointestinal Ca availability as well as blood Ca clearance in the transition dairy cow allowed us to conclude that the most common dietary strategies for milk fever prevention may have analogous modes of action that are based on the principle of metabolic adaptation before calving.

Expression patterns of intestinal calcium transport factors and ex-vivo absorption of calcium in horses

Background

In many species, the small intestine is the major site of calcium (Ca²⁺) absorption. The horse differs considerably from most other species with regard to the physiology of its Ca²⁺ metabolism and digestion. Thus, this study was performed to get more information about the transcellular Ca²⁺ absorption in the horse.

Two mechanisms of intestinal Ca²⁺ absorption are described: the passive paracellular pathway and the active, vitamin D-dependent transcellular pathway. The latter involves the following elements: vitamin D receptors (VDR), transient receptor potential vanilloid channel members 5 and 6 (TRPV5/6), calbindin-D9k (CB), the Na/Ca exchanger (NCX1) and the plasma membrane Ca-ATPase (PMCA). The aim of the present study was to investigate the protein and mRNA expression patterns of VDR, CB and TRPV6 and the ex-vivo Ca²⁺ absorption in horses, assessed by qualitative and quantitative RT-PCR, western blot, immunohistochemistry and the Ussing chamber technique.

Results

Highest CB and TRPV6 mRNA levels were detected in the duodenum as compared to the middle parts of the jejunum and ileum and several sites of the large intestine. VDR mRNA levels did not change significantly throughout the intestine. TRPV5 mRNA was not detectable in the horse intestine. The highest VDR and CB protein levels were measured in the duodenum. Ussing chamber studies revealed ex-vivo Ca²⁺ absorption only in the duodenum, but not in cecum and specific sites of the colon.

Conclusion

The present findings suggest that TRPV6, CB and VDR may be involved in active intestinal Ca²⁺ absorption in horses, as described for other mammals. TRPV5 may not play a major role in this process. Furthermore, the expression patterns of these Ca²⁺ transport elements and the results of the Ussing chamber procedure indicate that a significant part of active intestinal Ca²⁺ absorption occurs in the duodenum in this species.

Influence of different calcium supplies and a single vitamin D injection on vitamin D receptor and calbindin D9k immunoreactivities in the gastrointestinal tract of goat kids

The purpose of this study was to investigate whether diets differing in Ca concentration would have an influence on vitamin D (VitD) receptor (VDR) and calbindin D9k (Calb9k) immunoreactivities in the gastrointestinal tract of growing goats. In addition, the effect of a single VitD injection was studied, to clarify whether exogenous VitD would further increase the active Ca absorption mechanisms. The hypothesis of the study was that reduced Ca intake would lead to greater active Ca absorption, and with that, to greater amounts of VDR and Calb9k immunoreactivities. The normal Ca kid group (according to age requirements) received 2.5 to 6 g of Ca/d, whereas the lesser Ca kid group (less than requirements) received 1.5 to 4 g of Ca/d from wk 6 (weaning) to 15 (slaughter). In addition, 5 and 6 goat kids, respectively, of each group (normal Ca kid group, lesser Ca kid group), were injected with VitD (0.05 mg of cholecalciferol/kg of BW) in wk 14 of life. Blood samples were taken in wk 14 and 15. Calcium and VitD (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) concentrations were determined in serum. Immediately after slaughter, the duodenum (DD) and rumen (RU) were mounted in conventional Ussing chambers. Unidirectional flux rates of Ca across gastrointestinal tissues were measured. Additionally, tissue specimens of the gastrointestinal tract were collected, and formaldehyde-fixed paraffin sections were used for VDR and Calb9k immunohistochemistry. In all kid groups, a net absorption in the RU and a net secretion of Ca in the DD were observed. Immunoreactions of VDR were greatest in the duodenal mucosa, whereas Calb9k immunoreactions were observed in the forestomach and intestinal tissues. The greatest expression was observed in the duodenal surface epithelium. Additionally, in the VitD-injected groups, an immunoreaction occurred in the jejunal superficial and basal glands and the ileal superficial epithelium. In contrast, the other groups showed no Calb9k immunoreactions at these sites. In conclusion, there is clear evidence for the RU as a main site for Ca absorption. The results of this study also indicate that VDR and Calb9k are highly expressed in the duodenal mucosa. The active absorption may not have such an important role in the DD because active transport was also evident in the RU. However, Calb9k expression seems to be stimulated by VitD administration.