Seiichi Ishizuka

Diabetic osteopenia and circulating levels of vitamin D metabolites in type 2 (noninsulin-dependent) diabetes

The degree of diabetic osteopenia and serum vitamin D metabolite levels were measured in 168 type 2 (noninsulin-dependent) diabetic patients. Based on six indices obtained by microdensitometry, we found the bone mass in 26.2% of diabetic patients to be clearly decreased and in 11.9% to be severely decreased. Our direct method of analysis of bone mass shows that diabetic osteopenia differs from typical osteoporosis in character. In addition, serum 24,25-dihydroxyvitamin D was significantly decreased (P less than 0.01), but 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were similar to those of controls.

Sarcoid granulomas metabolize 25-hydroxyvitamin D3invitro

Sarcoid granulomas metabolized 25-hydroxyvitamin D3 to two unidentified metabolites during in vitro incubation. A two-step high pressure liquid chromatography system revealed two unique elution positions of these sarcoid-derived metabolites that exactly comigrated with the elution positions of 5(Z)-19-nor-10-oxo-25(OH)D3 and 5(E)-19-nor-10-oxo-25(OH)D3, respectively. These unique metabolites did not bind specifically to a protein receptor for 1,25(OH)2D3.

Human myeloid leukemia cells metabolize 25-hydroxyvitamin D3 in vitro

Human promyelocytic leukemia cells (HL-60) converted 25-hydroxyvitamin D3 to two more polar metabolites during in vitro incubations. A two-step high pressure liquid chromatography system revealed two unique elution positions of those leukemic cell-derived metabolites that exactly co-migrated with the elution positions of 5(Z)-19-nor-10-oxo-25-hydroxyvitamin D3 and 5(E)-19-nor-10-oxo-25-hydroxyvitamin D3, respectively. These unique metabolites did not bind specifically to a protein receptor for 1,25-dihydroxyvitamin D3.

Intrinsic biological activities by 1α,24-dihydroxyvitamin D3 in the rat

Subcellular localization of [3H]1α,24(R)-dihydroxyvitamin D3 and [3H]1α,24(S)-dihydroxyvitamin D3 in rat intestinal mucosa was investigated in comparison with the [3H]1α-hydroxyvitamin D3. The 24(R) and 24(S) isomers of 1α,24-dihydroxyvitamin D3 were gradually transformed to 1α,24(R)25-trihydroxyvitamin D3 and 1α,24(S)25-trihydroxyvitamin D3, and the plasma concentrations of these metabolites were 10.30 and 1.36 pmol/ml, respectively. The major portions of the administered compounds distributed in the nuclear fraction of the intestinal mucosa remained unchanged, and the amounts of 1α,24(R)-dihydroxyvitamin D3 and 1α,24(S)-dihydroxyvitamin D3 were 4.25 and 0.306 pmol/g intestinal mucosa, respectively. No detectable amount of the metabolites, 1α,24(R)25-trihydroxyvitamin D3 and 1α,24(S)25-trihydroxyvitamin D3 were found in the same nuclear fractions. In the case with the [3H]1α-hydroxyvitamin D3, however, the compound was rapidly metabolized to 1α,25-dihydroxyvitamin D3. The metabolite, 1α,25-dihydroxyvitamin D3, was seen in the nuclear fraction of the intestinal mucosa at a concentration of 2.44 pmol/g intestinal mucosa.

Accumulation of cyclic guanosine 3′:5′-monophosphate in the culture medium of growing cells of Escherichia coli

Abstract In an exponentially growing culture of E. coli , the concentration of cyclic guanosine 3′:5′-monophosphate (cyclic GMP) was found to increase in parallel with the bacterial growth. As the cells approach the stationary phase of growth, the increment of cyclic GMP also ceases progressively to reach to a plateau. When cells are separated from the medium by centrifugation, almost all of the cyclic GMP is recovered in the culture supernatant. The amount of cyclic GMP accumulated is proportional to the number of cells present in the culture. These results suggest that a constant number of cyclic GMP molecules is synthesized each generation of E. coli , and is excreted from the cells to accumulate into the medium.

Studies on the mechanism of action of 1α,24-dihydroxyvitamin D3 III the specific binding of 1α,24-dihydroxyvitamin D3 to the receptor of chick parathyroid gland

Abstract Three protein fractions of the cytosol of the chick parathyroid glands, which had the sedimentation constants of 2.5 S, 3.7 S and 5.5 S, were found to bind with 1α, 25-dihydroxyvitamin D3. Among these proteins, the 3.7 S protein was assumed to be the specific receptor protein. The 3.7 S receptor protein was also capable of binding to 1α, 24-dihydroxyvitamin D3 but not 25-hydroxyvitamin D3. The binding affinity of 1α, 24(R)-dihydroxyvitamin D3 to the 3.7 S receptor protein was estimated to be 1.2 times greater than that of 1α,25-dihydroxyvitamin D3, while 1α,25-dihydroxyvitamin D3 bound to the receptor protein about 10 times stronger than 1α,24(S)-dihydroxyvitamin D3. The dissociation constant for, the receptor-1α, 25-dihydroxyvitamin D3 complex at 0°C was 2.7 × 10−11 M, the dissociation constants were calculated to be 2.2 × 10−11 M and 2.6 × 10−10 M for the complexes with 1α,24(R)-dihydroxyvitamin D3 and 1α,24(S)-dihydroxyvitamin D3, respectively.

In vitro 25-hydroxylation of 1α,24-dihydroxyvitamin D3 in various rat tissues

The 25-hydroxylation of vitamin Ds in the liver is the first step for vitamin Ds activation [l-3]. 25-OH-Ds was shown formed from vitamin Ds in intact rats but not to a signii&ant level in the hepatectomized rats [ 1,2]. This suggests that the transformation ofvitamin Da to 25-OH-Da takes place mainly, if not only, irt the liver ~ The tr~sfor~tion of &amin Da to 255H-Ds was demonstrated using both perfused rat liver and rat liver homogenate systems [31. However, vitamin D&Lhydroxylase activity was reported present in the kidney and intestine as well as in the liver of chick [4], indicating the distribution of the enzyme in various tissues. We have shown that lar,24(OHhDs is metabolized rapidly to lcw,24,25-(OH)sDa in rats [5,6] and the 25” hydroxylation occurs mainly in the liver [S]. However, the possibility of 25hydroxylation in the tissues other than the liver has been suggested also, since a small amount of laJ4,25-(OH)sDs was formed from la;24fOffaDs in the hepatecto~d rats. This paper describes the 25-hydroxylation of la@&Xl)sDs and la-OH-Da using homogenates of rat liver, kidney, intestine, bone, adrenal and muscle.