Regulation of 1,25-Dihydroxyvitamin D₃Production by Cultured Alveolar Macrophages from Normal Human Donors and from Patients with Pulmonary Sarcoidosis*

Abstract

Regulation of the production of the biologically active vitamin D3 sterol 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] by cultured pulmonary alveolar macrophages (PAM) obtained from 6 patients with pulmonary sarcoidosis and from 9 normal subjects was studied. The sarcoid cells, all collected from patients with normal calcium metabolism, synthesized 1,25-(OH)2-[3H]D3 from the substrate 25-hydroxyvitamin [3H]D3 (25OH-[3H]D3), whereas in vitro incubation with recombinant human interferon-gamma (IFN gamma) or lipopolysaccharide (LPS) was required for induction of synthesis of the hormone by normal PAM. Exogenous 1,25-(OH)2D3 (10-100 nmol/L) decreased endogenous hormone production by normal PAM by approximately 45%. The relative inhibitory effect of 1,25-(OH)2D3 was less pronounced in sarcoid PAM, in which 10-100 nmol/L 1,25-(OH)2D3 inhibited 250HD3-1-hydroxylase by approximately 25%. An accompanying induction of the 250HD3-24-hydroxylase, which is typical for renal cells, was found at low levels in only 3 of 10 experiments; in this regard, no differences between sarcoid and normal PAM were apparent. PTH or forskolin did not influence 250HD3 metabolism by PAM. 1,25-(OH)2D3 production by sarcoid PAM was enhanced by lipopolysaccharide and IFN gamma. Likewise, recombinant human interleukin-2 stimulated 1,25-(OH)2D3 production by sarcoid PAM, suggesting a possible role for both IFN gamma and interleukin-2 in the induction of 1,25-(OH)2D3 synthesis by sarcoid PAM in vivo. Recombinant human IFN alpha, IFN beta, and granulocyte-macrophage colony-stimulating factor had little effect. Dexamethasone and chloroquine, which have in vivo antihypercalcemic activity in sarcoidosis, both inhibited 1,25-(OH)2D3 synthesis by sarcoid PAM; chloroquine simultaneously stimulated the 24-hydroxylase. Our studies suggest that the 250HD3-metabolizing system in PAM is in some respects different from renal metabolism of 250HD3.

Stat1-Vitamin D Receptor Interactions Antagonize 1,25-Dihydroxyvitamin D Transcriptional Activity and Enhance Stat1-Mediated Transcription

“…In these patients, high levels of 1,25D in serum result from excessive 1,25D synthesis by the disease-activated macrophage (2,3,28) and loss of the capacity of 1,25D to regulate its own synthesis and degradation (16,42). The demonstration of a direct correlation between pleural levels of gamma interferon (IFN-␥) and 1,25D (2) suggested the involvement of the cytokine in the abnormalities in 1,25D homeostasis.…”

Hypercalcemia and soft tissue calcification owing to sarcoidosis: The sunlight-cola connection

“…(12) The enzyme is also less sensitive to product inhibition by 1,25(OH) 2 D than is the renal 1-hydroxylase. (13) PAMs from sarcoid patients constitutively produce 1,25(OH) 2 D (11) and can be further stimulated to produce 1,25(OH) 2 D by inflammatory mediators such as interleukin 2 (IL-2). (13) Why the body has developed a system of local 1,25 (OH) 2 D production in the setting of inflammation is unclear, but there is evidence to suggest that 1,25(OH) 2 D may modulate local inflammation and immunity.…”

“…(13) PAMs from sarcoid patients constitutively produce 1,25(OH) 2 D (11) and can be further stimulated to produce 1,25(OH) 2 D by inflammatory mediators such as interleukin 2 (IL-2). (13) Why the body has developed a system of local 1,25 (OH) 2 D production in the setting of inflammation is unclear, but there is evidence to suggest that 1,25(OH) 2 D may modulate local inflammation and immunity. 1,25(OH) 2 D suppresses proliferation of T-helper 1 cells that make interferon g (IFN-g) and IL-2 and activate macrophages.…”

“…(19) In 1987, Reichel and colleagues demonstrated that dexamethasone suppressed 1,25(OH) 2 D production in cultured PAMs. (13) There are no randomized, controlled trials to guide dosing of steroids for sarcoid-induced hypercalcemia. One approach is to use the recommended doses for pulmonary sarcoid, 20 to 40 mg of prednisone once daily or its equivalent every other day.…”

“…While the exact mechanism by which chloroquine reduces 1,25(OH) 2 D levels is unknown, it may impair granuloma formation. (22,23) Reichel and colleagues showed that chloroquine may induce 24-hydroxylase activity, thereby inactivating both 25(OH)D and 1,25(OH) 2 D. (13) The onset of action of chloroquine is slower than that of corticosteroids, but its effect may be more durable. In several case reports, serum calcium normalized within several weeks to months.…”