Dusso A S, Finch J, Brown A, Ritter C, Delmez J, Schreiner G, Slatopolsky E
Renal Division, Washington University School of Medicine, St. Louis, Missouri 63110.
J Clin Endocrinol Metab. 1991 Jan;72(1):157-64. doi: 10.1210/jcem-72-1-157.
We have previously reported low serum levels of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and increased 1,25-(OH)2D3 production after the administration of 25-hydryoxyvitamin D (25OHD) to anephric humans. Since normal alveolar macrophages are known to synthesize 1,25-(OH)2D3 when stimulated with gamma-interferon or lipopolysaccharide, we determined whether macrophages derived from peripheral blood monocytes could be an extrarenal source of 1,25-(OH)2D3. Our results demonstrated that macrophages from normal individuals synthesize 1,25-(OH)2D3. The apparent Km for 25OHD3 was 6.6 +/- 0.5 nM and the maximum velocity was 47.4 +/- 13.7 fmol 1,25-(OH)2D3/h.microgram DNA. The activity of this enzyme was reduced 37.2 +/- 3.1% by physiological concentrations (96 pmol/L) of 1,25-(OH)2D3 in the incubation medium. Normal macrophages further hydroxylated 1,25-(OH)2D3 to more polar metabolites, and this catabolic activity was significantly enhanced by physiological concentrations of 1,25-(OH)2D3. In chronic renal failure, peripheral macrophages exhibited an enhanced 1 alpha-hydroxylase activity (8.2 +/- 0.8 vs. 4.2 +/- 0.5 fmol 1,25-(OH)2D3/microgram DNA.h in controls) and a decreased capacity to degrade 1,25-(OH)2D3. Exogenous 1,25-(OH)2D3, in physiological concentrations, reduced 1,25-(OH)2D3 synthesis to a degree (23.6 +/- 8.5%) comparable to that observed in normal cells. 1,25-(OH)2D3 production by macrophages did not correlate with the severity of hyperparathyroidism. Moreover, human PTH-(1-34) in supraphysiological concentrations (20,000 and 100,000 ng/L) did not stimulate the 1 alpha-hydroxylase activity of macrophages from either normal or uremic subjects. These results demonstrate that 1) normal peripheral macrophages metabolize 25OHD3 and 1,25-(OH)2D3; 2) macrophages in uremia display higher rates of 1,25-(OH)2D3 synthesis and lower rates of catabolism than normal macrophages; and 3) 1,25-(OH)2D3 deficiency, but not hyperparathyroidism, may play a role in the stimulation of 1,25-(OH)2D3 production by macrophages in chronic renal failure.
我们之前曾报道，无肾患者血清中1,25 - 二羟基维生素D3 [1,25-(OH)2D3] 水平较低，且给予25 - 羟基维生素D（25OHD）后1,25-(OH)2D3的生成增加。由于已知正常肺泡巨噬细胞在受到γ-干扰素或脂多糖刺激时可合成1,25-(OH)2D3，我们确定外周血单核细胞衍生的巨噬细胞是否可能是1,25-(OH)2D3的肾外来源。我们的结果表明，正常个体的巨噬细胞可合成1,25-(OH)2D3。25OHD3的表观米氏常数为6.6±0.5 nM，最大反应速度为47.4±13.7 fmol 1,25-(OH)2D3/小时·微克DNA。在孵育培养基中，生理浓度（96 pmol/L）的1,25-(OH)2D3可使该酶的活性降低37.2±3.1%。正常巨噬细胞可将1,25-(OH)2D3进一步羟化为极性更强的代谢产物，且生理浓度的1,25-(OH)2D3可显著增强这种分解代谢活性。在慢性肾衰竭患者中，外周巨噬细胞表现出增强的1α-羟化酶活性（对照组为4.2±0.5 fmol 1,25-(OH)2D3/微克DNA·小时，慢性肾衰竭患者为8.2±0.8）以及降低的1,25-(OH)2D3降解能力。生理浓度的外源性1,25-(OH)2D3可使1,25-(OH)2D3的合成降低一定程度（23.6±8.5%），与正常细胞中观察到的情况相当。巨噬细胞产生1,25-(OH)2D3的量与甲状旁腺功能亢进的严重程度无关。此外，超生理浓度（20,000和100,000 ng/L）的人甲状旁腺激素（PTH）-(1 - 34) 不会刺激正常或尿毒症患者巨噬细胞的1α-羟化酶活性。这些结果表明：1）正常外周巨噬细胞可代谢25OHD3和1,25-(OH)2D3；2）与正常巨噬细胞相比，尿毒症患者的巨噬细胞1,25-(OH)2D3合成速率更高，分解代谢速率更低；3）1,25-(OH)2D3缺乏而非甲状旁腺功能亢进可能在慢性肾衰竭中刺激巨噬细胞产生1,25-(OH)2D3的过程中起作用。
