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Original Studies |
Department of Clinical and Laboratory Medicine (M.N., M.U., A.N., K.O., M.Y.) and the First Department of Internal Medicine (K.N.), Kyoto Prefectural University of Medicine, Kyoto 602; and the Department of Clinical Sciences and Laboratory Medicine, Kansai Medical University (H.T.), Osaka 570, Japan
Address all correspondence and requests for reprints to: Masato Nishimura, M.D., Department of Clinical and Laboratory Medicine, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Kawaramachi-Hirokoji, Kamikyo-ku, Kyoto 602, Japan.
| Abstract |
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| Introduction |
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-chain and a 34-kDa ß-chain (7, 8). The HGF
receptor is the c-met protooncogene product, a transmembrane
tyrosine kinase (9). Although HGF has been well characterized as a
hepatotropic (10, 11) and a renotropic factor (12, 13) in liver and
kidney regeneration, the presence of the local HGF system (HGF and its
receptor, c-met) has been demonstrated in both endothelial
cells and vascular smooth muscle cells in vivo and in
vitro (14). Recent studies indicate that human HGF (hHGF) is a
powerful inducer of angiogenesis (15, 16). Moreover, hHGF may
contribute to the genesis of acquired immunodeficiency
syndrome-associated Kaposis sarcoma, a cytokine-dependent neoplasm
characterized by a major component of neovascularization (17). Although
a relationship between hHGF and neovascularization in PDR has never
been reported, hHGF may be involved in the pathogenesis of this
disorder. In this study we investigated whether serum hHGF
concentrations may indicate the presence of PDR in diabetic patients by
studying the relationship between serum concentrations of hHGF and the
degree of diabetic retinopathy. | Subjects and Methods |
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Data are expressed as the mean ± SEM. The significance of differences between groups was evaluated by one-way of ANOVA followed by Duncans multiple range test. Simple regression analyses were used to assess the relationship between hHGF and other parameters. The criterion for statistical significance was P < 0.05.
| Results |
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The mean serum concentration of hHGF was lower in the diabetic
patients with NDR than in nondiabetic subjects (0.041 ± 0.003
vs. 0.080 ± 0.010 ng/mL; P < 0.05;
Fig. 1
). The mean serum hHGF
concentration was not different among the diabetic patients of the NDR,
BDR (0.058 ± 0.007 ng/mL), and Pre-PDR (0.048 ± 0.010
ng/mL) groups; however, it was higher in the PDR group (0.213 ±
0.025 ng/mL) than in the nondiabetic control subjects or the NDR, BDR,
or Pre-PDR group. The mean serum hHGF concentration in the PC-PDR group
(0.040 ± 0.008 ng/mL) was lower than that in the PDR group and
was at the same level as those in the NDR, BDR, and Pre-PDR groups.
Serum hHGF concentrations higher than 0.1 ng/mL were found in 19 of 80
subjects (23.8%) in the nondiabetic control group, 2 of 62 (3.2%) in
the NDR group, 3 of 26 (11.5%) in the BDR group, and 17 of 24 (70.8%)
in the PDR group, but were not found in any subjects in the Pre-PDR and
PC-PDR groups. In addition, serum hHGF concentrations higher than 0.15
ng/mL were not observed in the diabetic patients except in the PDR
group, in which serum HGF concentrations were over 0.15 ng/mL in 16 of
24 subjects (66.7%). Serum hHGF concentrations higher than 0.15 ng/mL
were observed in 10 of 80 subjects (12.5%) in the nondiabetic control
group. In the PDR group, diastolic blood pressure levels were higher
(P < 0.05) in the subgroup in which serum hHGF
concentrations were below 0.15 ng/mL (84 ± 3 mm Hg; n = 8)
than in the subgroup in which serum hHGF levels were above 0.15 ng/mL
(75 ± 2 mm Hg; n = 16). Age [64 ± 3 yr (n = 8)
vs. 61 ± 3 yr (n = 16)], systolic blood pressure
[144 ± 6 mm Hg (n = 8) vs. 138 ± 6 mm Hg
(n = 16)], fasting serum glucose concentration [136 ± 19
mg/dL (n = 8) vs. 141 ± 9 mg/dL (n = 16)],
serum concentrations of hemoglobin A1c [8.2 ± 0.4%
(n = 8) vs. 7.9 ± 0.3% (n = 16)], and uric
acid [4.7 ± 0.5 mg/dL (n = 8) vs. 5.2 ±
0.4 mg/dL (n = 16)] or duration of diabetes [19 ± 2.5 yr
(n = 8) vs. 21 ± 1.9 yr (n = 16)] were not
different between these two subgroups of PDR.
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In the nondiabetic control group, the serum hHGF concentration was
positively correlated with the serum concentration of uric acid, but
not with age or blood pressure (Table 2
).
The serum hHGF concentration was positively correlated with the serum
uric acid concentration or the duration of the disease in the diabetic
patients without a history of photocoagulation, whereas the serum uric
acid concentration was not correlated with serum hHGF in the PC-PDR
group.
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Diabetes mellitus was treated by diet therapy alone (n =
17), oral antidiabetic drugs [total n = 51; sulfonylurea
(n = 40);
-glucosidase inhibitor (n = 4), biguanide
(n = 1), sulfonylurea plus
-glucosidase inhibitor (n =
6)], insulin injection (n = 45), or insulin plus oral
antidiabetic drugs [total n = 22; sulfonylurea (n = 12),
-glucosidase inhibitor (n = 9), biguanide (n = 1)]. The
mean serum hHGF concentration was not different among patients treated
with diet (0.037 ± 0.007 ng/mL), oral antidiabetic drugs
(0.079 ± 0.014 ng/mL), insulin (0.083 ± 0.013 ng/mL), and
insulin plus oral antidiabetic drugs (0.082 ± 0.016 ng/mL).
| Discussion |
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Serum hHGF concentrations in nondiabetic control subjects were distributed over a range between 0.006 and 0.364 ng/mL. Because control subjects were selected carefully in present study, this broad distribution of serum hHGF concentrations does not derive from any medical disorder in control subjects; it may indicate the influence of substances that affect serum hHGF levels, such as a novel serine protease that is responsible for activation of HGF (25). We need further investigation to clarify the regulatory mechanism of the circulating hHGF concentration.
The difference in serum hHGF concentrations between patients with PDR and those with PC-PDR, in which neovascularization subsides, suggests that neovascularization in the retina involves an increase in serum hHGF concentrations in patients with PDR. In vitro, HGF stimulates endothelial migration in Boyden chambers (26) and formation of capillary-like tubules (27). Physiological quantities of purified native mouse HGF and recombinant hHGF have been reported to induce angiogenesis in vivo, and immunoreactive hHGF has been demonstrated in sites surrounding blood vessel formation in psoriatic skin (16). hHGF is likely to be involved in retinal neovascularization, which is a compensatory adaptation for retinal ischemia and a major characteristic of PDR.
The plasma half-life of HGF is reported to be 4 min in rats (28). This rather short half-life and high time difference reproducibility of serum hHGF values in our enzyme-linked immunosorbent assay method (96.7 ± 9%) indicate that hHGF is constitutively secreted into the circulation. Two hypotheses may explain the increased concentrations of serum hHGF in the PDR subjects. One is that hHGF production may be enhanced in extraocular organs such as liver, kidney, lung, or spleen to promote neovascularization in the retina. After 70% partial hepatectomy in rats, HGF messenger ribonucleic acid levels in kidney and spleen increase 3- to 5-fold (29), and HGF messenger ribonucleic acid in spleen is increased after the onset of renal injury caused by unilateral nephrectomy (30). HGF produced in the uninjured organs may be involved in regeneration of liver or kidney through an endocrine mechanism (31). The same endocrinological mechanism may play a role in the increased concentrations of serum hHGF in PDR subjects. Another possibility is that hHGF production may have been enhanced in the eyes of PDR patients. The hHGF concentrations in the human vitreous body are 50- to 100-fold higher than the serum concentrations and are higher in diabetic patients with PDR than in nondiabetic patients (our unpublished observation). Increased concentrations of serum hHGF in PDR patients are likely to originate from enhanced production of hHGF in the eye with neovascularization.
Serum hHGF concentrations were correlated not with age or blood pressure, but with serum concentrations of uric acid in nondiabetic and diabetic subjects, in agreement with our recent observation in healthy subjects (32). No significant correlation of serum hHGF with serum concentrations of hemoglobin A1c or fasting glucose in diabetic subjects indicates that diabetic control does not necessarily have an influence on serum hHGF concentrations, although hyperglycemia may inhibit the production of hHGF via TGFß, as described above. The significant correlation between serum hHGF and duration of diabetes may reflect the involvement of systemic microvascular complications, including PDR, in serum hHGF concentrations in diabetic subjects, although further studies are needed to clarify this point.
The results in the present study suggest that diabetic patients whose serum hHGF concentrations are over 0.15 ng/mL may have PDR and need detailed ophthalmologic examination, although concentrations of serum hHGF below 0.15 ng/mL do not necessarily exclude the existence of PDR. Moreover, serum hHGF concentrations higher than 0.1 ng/mL in diabetic patients with a history of photocoagulation are likely to suggest the reappearance of retinal neovascularization. Measurement of serum hHGF concentrations may be helpful to predict the presence of PDR in patients with diabetes mellitus.
Received June 23, 1997.
Revised August 19, 1997.
Accepted September 24, 1997.
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