Shortcomings of vitamin D-based model simulations of seasonal influenza

Seasonal variation in serum concentration of the vitamin D metabolite 25(OH) vitamin D [25(OH)D], which contributes to host immune function, has been hypothesized to be the underlying source of observed influenza seasonality in temperate regions. The objective of this study was to determine whether observed 25(OH)D levels could be used to simulate observed influenza infection rates. Data of mean and variance in 25(OH)D serum levels by month were obtained from the Health Professionals Follow-up Study and used to parameterize an individual-based model of influenza transmission dynamics in two regions of the United States. Simulations were compared with observed daily influenza excess mortality data. Best-fitting simulations could reproduce the observed seasonal cycle of influenza; however, these best-fit simulations were shown to be highly sensitive to stochastic processes within the model and were unable consistently to reproduce observed seasonal patterns. In this respect the simulations with the vitamin D forced model were inferior to similar modeling efforts using absolute humidity and the school calendar as seasonal forcing variables. These model results indicate it is unlikely that seasonal variations in vitamin D levels principally determine the seasonality of influenza in temperate regions.     

The renal sensitivity for endogenous parathormone in patients with primary hyperparathyroidism, vitamin D deficiency and renal stones

Baseline levels and increases in urinary cyclic AMP excretion (UcAMP) and immunoreactive parathormone (iPTH) were studied before and during infusion of EDTA in euparathyroid patients with renal stones (n=11), patients with primary hyperparathyroidism (PHP; n=14) and patients with vitamin D deficiency (n = 12). In all three groups, EDTA evoked a significant rise in iPTH and UcAMP. In patients with PHP and in those with vitamin D deficiency, there was a sufficiently close relationship between increments in iPTH (delta iPTH) and in UcAMP (delta UcAMP) (r = 0.90, P less than 0.001 and r = 0.67, P less than 0.02, respectively) to use this model to assess renal sensitivity for changes to endogenous PTH levels. We quantified sensitivity of the kidney for PTH, by calculating the ratio delta UcAMP/delta TPTH for the three studied groups. The ratio was comparable in patients with renal stones (16.7 +/- 10.3) and PHP (13.8 +/- 4.9, P greater than 0.10), but was significantly increased in patients with vitamin D deficiency (33.2 +/- 17.9; P less than 0.01 versus patients with renal stones and P less than 0.01 versus patients with PHP). Within the group of patients with PHP there was no correlation between baseline serum calcium concentrations and the ratio delta UcAMP/delta TPTH. It is concluded that in patients with vitamin D deficiency, renal sensitivity to PTH is increased compared with patients with PHP and euparathyroid patients with renal stones, perhaps an expression of a teleological useful adaptation of end organ sensitivity.     

Synthesis and evaluation of vitamin D-based cationic lipids for gene delivery in vitro

A new panel of steroidal cationic lipids has been synthesized for gene delivery. Using commercially available vitamin D2 (calciferol) or vitamin D3 (cholecalciferol) as hydrophobic motifs and a variety of cationic head groups as binding sites for negatively charged phosphate groups in DNA, we demonstrated that the transfection activity of the synthetic vitamin D-based cationic lipids 1d, 2d formulated with dioleoylphosphatidylethanolamine (DOPE) as a co-lipid is comparable to that of 3-(-[N-N',N'-dimethylaminoethane)carbamoyl]cholesterol (DC-Chol). These synthetic lipids are effective in transfecting a variety of cell lines. These results suggest that vitamin D-based cationic lipids are useful transfection reagents for in vitro gene transfer studies.     

Pathophysiology of primary hyperparathyroidism

Parathyroid gland is the overall regulatory organ within the systemic calcium homeostasis. Through cell surface bound calcium-sensing receptors external calcium inversely regulates release of parathyroid hormone (PTH). This mechanism, which is voltage independent and most sensitive around physiologic calcium concentrations, is regulated through a 120 kDa calcium sensing receptor, CaR. Inherited inactivation of this receptor is the cause for familial hypocalciuric hypercalcemia (FHH). Parallel research identified the 550 kDa glycoprotein megalin, which also is expressed on the parathyroid cell surface, as another potential calcium sensing protein. Although this protein expresses numerous calcium binding sites on its external domain, its main function may be calcium sensitive binding and uptake of steroid hormones, such as 25-OH-vitamin D3 (bound to vitamin D binding protein) and retinol. In hyperparathyroidism (HPT), excessive PTH is secreted and the calcium sensitivity of the cells reduced, i.e. the set-point, defined as the external calcium concentration at which half-maximal inhibition of PTH release occurs, shifted to the right. Pathological cells have reduced expression of both CaR and megalin, and reduced amount of intracellular lipids, possibly including stored steroid hormones. A number of possible genetic disturbances have been identified, indicating multifactorial reasons for the disease. In postmenopausal women, however, the individual group with highest incidence of disease, a causal relation to reduced effect of vitamin D is possible. An incipient renal insufficiency with age, lack of sunshine in the Northern Hemisphere, and an association to the baT haplotype of the vitamin D receptor supports this theory. This review summarizes data on regulation of PTH release, dysregulation in HPT, as well as proliferation of parathyroid cells.     

A case of normocalcemic primary hyperparathyroidism with osteomalacia

A 59 year-old patient had lumbago and pain in hip joints, knees, and ribs of long duration. Severe hypophosphatemia and high serum ionized calcium were found in spite of normal level of total serum calcium. The serum parathyroid hormone and alkaline phosphatase levels were elevated, and diffuse demineralization of the bones and renal stones were found by x-ray examination. Parathyroid adenoma was diagnosed from the subtraction image of the 99mTc O-4 and 201Tl-Cl2 scintigrams. Osteomalacia was demonstrated by bone biopsy at the right iliac crest. A right lower parathyroid adenoma of 2.0 X 1.8 cm, weighing 4.0 g was removed. The long standing phosphate depletion and hypophosphatemia, due to hyperparathyroidism causing renal damage with nephrocalcinosis and reduced synthesis of active vitamin D, and milk tolerance due to gastroduodenostomy were probably responsible for producing the clinical picture of normocalcemic hyperparathyroidism complicated with osteomalacia.     

Value of 1-alpha-hydroxy vitamin D3 in treatment of primary hyperparathyroidism before parathyroidectomy.

The postoperative course of six patients with primary hyperparathyroidism and obvious radiological evidence of bone disease pretreated with 1-alpha-hydroxy vitamin D3 (1 alpha HCC) was indistinguishable from that of six patients with a similar clinical and radiological picture who were not pretreated. 1alphaHCC may increase the hypercalcaemia in some cases and cannot be recommended for the routine preparation of such patients for surgery.     

Possibilities and limits of the medical treatment for primary hyperparathyroidism

Clinically obvious primary hyperparathyroidism is only curable by surgery. Medical treatment is debatable under other circumstances: mild chronic hypercalcemia, patients who refuse surgery, serious coexisting medical problems and recurrence or persistence of PHPT after surgical treatment. Prior to medical treatment, the usual common management of any mild hypercalcemia must be taken. The potential medical treatments are: (1) the inhibition of parathyroid hormone (PTH) secretion, and (2) the inhibition of the effects of PTH. The substances of these two main types are successively described. Nevertheless, no ideal medical treatment of PHPT is actually available.     

Arterial structure and function in mild primary hyperparathyroidism is not directly related to parathyroid hormone, calcium, or vitamin D

Objective

Elevated levels of calcium and parathyroid hormone (PTH), characteristics of primary hyperparathyroidism (PHPT), may be associated with cardiovascular morbidity and mortality in the general population. We evaluated the possible vascular effects of these risk factors in patients with mild PHPT by using standard methods and new imaging techniques.

Design

A prospective case-control study.

Subjects and Methods

Forty-eight patients with mild PHPT without any known cardiovascular risk factors were studied at baseline and at one year after parathyroidectomy (PTX) in comparison with 48 healthy age- and gender-matched controls. We measured biochemical variables, augmentation index (AIx), aortic pulse wave velocity (PWV_ao), radial (IMT_rad) and common carotid artery (IMT_cca) intima media thicknesses, and the grayscale median (IM-GSM) of the latter.

Results

No significant differences were observed between PHPT patients and controls at baseline for AIx (28.6±12.2 vs. 27.7±12.8%), IMT_rad (0.271±0.060 vs. 0.255±0.053 mm), IMT_cca (0.688±0.113 vs. 0.680±0.135 mm), or IM-GSM (82.3±17.2 vs. 86.5±15.3), while PWV_ao was slightly higher in patients (8.68±1.50 vs. 8.13±1.55, p<0.05). Systolic blood pressure (SBP), calcium, and PTH were higher in patients compared with controls, and decreased after PTX, while vitamin D was lower in patients and increased after PTX. While AIx, PWV_ao, IMT_rad, and IMT_cca were related to SBP, neither correlated to vitamin D levels. Only PWV_ao correlated weakly to plasma PTH (r = 0.29, p<0.01) and ionized calcium (r = 0.22, p<0.05) but showed no relation when age and SBP were adjusted for.

Conclusion

We found normal arterial function despite high calcium, PTH, and low vitamin D levels, in patients with mild PHPT without cardiovascular risk factors. The cardiovascular risk associated with low vitamin D and/or high PTH and calcium levels may be explained by their coupling to blood pressure and other risk factors rather than direct effects on arterial structure.     

Bone fracture in elderly female with primary hyperparathyroidism: relationship among renal function, vitamin D status and fracture risk

Among 12 aged postmenopausal females with primary hyperparathyroidism, 5 had no bone fracture and 7 had fractures. Both serum 1,25 (OH)2D levels and creatinine clearance values in patients with fracture were significantly lower than those without fracture (p less than 0.025). In addition, significant positive correlation was observed between serum 1,25 (OH)2D levels and creatinine clearance values (p less than 0.05). These data suggest that decreased serum 1,25 (OH)2D level due to renal dysfunction may causally correlate to bone fracture in postmenopausal primary hyperparathyroidism.     

The chloride phosphate ratio as the screening test for primary hyperparathyroidism

Serum chloride and phosphate concentrations were measured in 79 hypercalcemic patients. The chloride values were higher (mean 106.7 mEq/l) and phosphate lower (mean 2.08 mg/100 ml) in the 53 hyperparathyroid patients, where as the chloride concentrations were lower (mean 99.3 mEq/l) and phosphate higher (mean 4.07 mg/100 ml) in the 26 patients with hypercalcemia from other causes. The chloride phosphate ratio ranged from 19 to 32 in the subjects with hypercalcemia from other causes with 90 per cent of values less than 30. In patients with primary hyperparathyroidism we found 96 per cent of the values more than 34. From our experience with chloride phosphate ratio it seems to us that this ratio is a very useful and simple preliminary test for distinguishing patients with primary hyperparathyroidism from patients with hypercalcemia from other causes, with normal renal functions.