Vitamin D binding globulin levels and affinity in various clinical conditions

The Role of Vitamin D and Vitamin D Binding Protein in Chronic Liver Diseases

Vitamin D (calciferol) is a fat-soluble vitamin that has a significant role in phospho-calcium metabolism, maintaining normal calcium levels and bone health development. The most important compounds of vitamin D are cholecalciferol (vitamin D3, or VD3) and ergocalciferol (vitamin D2, or VD2). Besides its major role in maintaining an adequate level of calcium and phosphate concentrations, vitamin D is involved in cell growth and differentiation and immune function. Recently, the association between vitamin D deficiency and the progression of fibrosis in chronic liver disease (CLD) was confirmed, given the hepatic activation process and high prevalence of vitamin D deficiency in these diseases. There are reports of vitamin D deficiency in CLD regardless of the etiology (chronic viral hepatitis, alcoholic cirrhosis, non-alcoholic fatty liver disease, primary biliary cirrhosis, or autoimmune hepatitis). Vitamin D binding protein (VDBP) is synthesized by the liver and has the role of binding and transporting vitamin D and its metabolites to the target organs. VDBP also plays an important role in inflammatory response secondary to tissue damage, being involved in the degradation of actin. As intense research during the last decades revealed the possible role of vitamin D in liver diseases, a deeper understanding of the vitamin D, vitamin D receptors (VDRs), and VDBP involvement in liver inflammation and fibrogenesis could represent the basis for the development of new strategies for diagnosis, prognosis, and treatment of liver diseases. This narrative review presents an overview of the evidence of the role of vitamin D and VDBP in CLD, both at the experimental and clinical levels.

Association between ambient carbon monoxide and secondary hyperparathyroidism in nondiabetic patients undergoing peritoneal dialysis

Background

Secondary hyperparathyroidism (SHPT) is a major disorder in patients with chronic renal disease with or without dialysis. Air pollution has been confirmed as being associated with increased incidence of human morbidity and mortality. To our knowledge, investigating air pollution as a dialysis-unrelated factor for SHPT in patients undergoing dialysis is limited. We developed this study to assess the effect of air pollution and other important risk factors on SHPT in patients undergoing peritoneal dialysis (PD).

Materials and methods

We recruited a total of 141 patients who did not have diabetes mellitus, were nonsmokers, and were undergoing PD in this cross-sectional study. We analyzed the difference in air quality based on the patients’ living areas. We estimated demographic, hematological, nutritional, inflammatory, biochemical, air pollutant, and dialysis-related data based on this cross-sectional study. Subgroup analysis of the relationship between air pollutants and the clinical variables and having or not having hyperparathyroidism (HPT) (intact parathyroid hormone level ≥180 pg/dL) was also performed.

Results

A total of 141 patients undergoing PD (30 men and 111 women) were enrolled in the study. Sixty-eight patients had SHPT. In a binary logistic regression, high environmental CO exposure (odds ratio [OR] 3.22, 95% confidence interval [CI] 1.42–7.28; P=0.005), serum phosphate levels (OR 1.66, 95% CI 1.17–2.37; P=0.005), hypoalbuminemia (OR 3.76, 95% CI 1.29–10.94; P=0.015), and use of calcitriol (OR 8.25, 95% CI 3.43–19.85; P<0.001) were positively associated with SHPT.

Conclusion

The findings of this cross-sectional study indicated the presence of an association between environmental CO exposure and SHPT in patients undergoing PD who did not have diabetes mellitus. Therefore, poor environmental air quality may be a risk factor for deterioration of SHPT in patients undergoing PD.

Serum concentrations of 25-hydroxyvitamin D and vitamin D-binding protein in elderly people. Effects of institutionalization, protein-energy malnutrition and inflammation

Serum concentrations of 25-hydroxyvitamin D (25-OH-D) and vitamin D-binding protein (DBP) were measured in institutionalized and non-institutionalized elderly people. The institutionalized subjects were found to have low serum 25-OH-D in confirmation of other studies, but their serum DBP levels were similar to those found in non-institutionalized elderly subjects. Serum DBP concentrations were slightly higher in elderly females than in males, while no age dependence was found for DBP. Elderly people with protein-energy malnutrition who lived in their own homes had slightly reduced serum DBP and 25-OH-D levels. Elderly subjects with infections or other diseases causing acute inflammation, as indicated by an elevated serum haptoglobin and C-reactive protein, had normal levels of DBP.

Glomerular protein sieving and implications for renal failure in Fanconi syndrome

BACKGROUND

Glomerular sieving coefficients (GSCs) of proteins have been measured extensively in animals but not humans. We have studied the proteinuria of Fanconi syndrome, a "knock-out" of renal tubular protein reabsorption, to estimate GSCs and detect potential contributors to development of renal failure.

METHODS

Immunoassay of proteins and polypeptides in serum and urine of patients with early Dent's disease (mean GFR = 83 mL/min, range 60 to 101, N = 5), Lowe's syndrome (N = 3), and ADIF (N = 2) were used.

RESULTS

Twenty-one proteins, ranging in mass from insulin (5.1 kD) and parathyroid hormone (PTH; 9.4 kD) to transferrin (78 kD) and intact IgG (160 kD), were present in Fanconi urine at> 6 to 1000-fold normal. A simple model assuming complete "knock-out" of the reuptake of each protein filtered normally by the glomerulus was applied to protein excretion by Dent's patients. GSCs were estimated for 12 plasma proteins, including albumin (7.7 +/- 0.9 x 10-5) and IgG (4.2 +/- 0.28 x 10-5; mean +/- SEM). We calculated the albumin concentration in normal glomerular filtrate to be 3.5 +/- 0.41 mg/L (53 +/- 6.4 nmol/L), consistent with studies in rat and dog.

CONCLUSIONS

To our knowledge, this study provides the first estimates of human in vivo GSCs. Our model explains why tubular proteinuria of Fanconi syndrome includes proteins of mass of albumin and above as well as low-molecular-weight proteins, and further characterizes the endocytic pathway(s) believed defective in these syndromes. High urinary concentrations of potentially bioactive hormones such as PTH, insulin, IGF-1 and the chemokine monocyte chemoattractant protein-1 (MCP-1), were found; their presence in tubular fluid may contribute to the hypercalciuria, interstitial fibrosis, and the progressive renal failure of Fanconi syndromes.

The effect of trauma on serum concentrations of vitamin D metabolites in patients with hip fracture

In a previous study we observed lower serum concentrations of 25(OH)D, 24,25(OH)2D, and 1,25(OH)2D in patients with hip fracture than in aged control subjects. In order to evaluate the effect of trauma on vitamin D metabolite levels, we measured serum concentrations of vitamin D binding protein (DBP) in 118 patients with hip fracture and 71 aged control subjects. Serum DBP was lower in the patients than in the controls (mean +/- SD 315 +/- 60 vs 371 +/- 44 mg/l, P less than 0.001). Serum DBP correlated positively with serum total protein, albumin, alpha 2-globulin, and the vitamin D metabolite levels in the patients. When correcting for differences in serum DBP, serum 25(OH)D and 24,25(OH)2D still were significantly lower in patients than in controls, whereas serum 1,25(OH)2D was not. The free 1,25(OH)2D index (10(5) x molar ratio 1,25(OH)2D/DBP) was lower in patients than in controls, but the level of significance was marginal. This difference was not significant when patients and controls with impairment of renal function were excluded. It is concluded that the difference in serum 25(OH)D and 24,25(OH)2D between patients and controls is largely preexistent. However, the lower serum 1,25(OH)2D in the patients is mainly caused by the trauma. The free 1,25(OH)2D concentrations are almost similar in the two groups when renal function is normal.