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Aims/hypothesis: Diabetes accelerates cardiovascular disease caused by atherosclerosis. Accordingly, diabetes accelerates atherosclerotic lesion progression and increases arterial smooth muscle cell proliferation. We hypothesized that diabetes can exert growth-promoting effects on smooth muscle cells via increased advanced glycation end-products or by dyslipidaemia., Methods: Primary human arterial smooth muscle cells were stimulated with advanced glycation end-products, other ligands of the receptor for advanced glycation end-products or fatty acids common in triglycerides. Cell proliferation was measured as DNA synthesis, cell cycle distribution and cell number. Effects of oleate on cellular phospholipids, diacylglycerol, triglycerides and cholesterol esters were analyzed by thin-layer chromatography, and oleate accumulation into diacylglycerol was confirmed by gas chromatography., Results: Human arterial smooth muscle cells express the receptor for advanced glycation end-products, but its ligands N(epsilon)-(carboxymethyl)lysine-modified proteins, methylglyoxal-modified proteins, S100B polypeptide and amyloid-beta (1-40) peptide, exert no mitogenic action. Instead, oleate, one of the most common fatty acids in triglycerides, enhances platelet-derived growth factor-BB-mediated proliferation and oleate-containing 1,2-diacylglycerol formation in smooth muscle cells. This mitogenic effect of oleate depends on phospholipase D activity and is associated with an increased formation of oleate-enriched 1,2-diacylglycerol., Conclusion/interpretation: Oleate, not ligands of the receptor for advanced glycation end-products, acts as an enhancer of human smooth muscle cell proliferation. Thus, lipid abnormalities, rather than hyperglycaemia, could be a major factor promoting proliferation of smooth muscle cells in atherosclerotic lesions.

The roles of diabetes mellitus, insulin-like growth factor I and insulin in vascular smooth muscle proliferation in vivo were studied. Proliferation was induced by endothelial injury (balloon catheterization) of rat aorta, and was measured as 3H-thymidine incorporation into DNA. Levels of insulin-like growth factor I mRNA and insulin-like growth factor I receptor mRNA were measured with a solution hybridization assay. The increase in DNA synthesis was most pronounced 2 days after injury in both normal and diabetic rats and declined thereafter, but DNA synthesis in aortas from diabetic rats was lower throughout the time period studied. Levels of insulin-like growth factor I mRNA and the receptor mRNA were both increased in balloon catheterized aortas, and time-course studies showed an increase in receptor mRNA prior to the increase in insulin-like growth factor I mRNA. Diabetic rats were treated with equimolar concentrations of insulin (35 nmol/day) or insulin-like growth factor I (31 nmol/day) for 5 days. Insulin-like growth factor I increased DNA synthesis in injured aortas 2 days after injury without improving blood glucose, whereas the effect of insulin was associated with a decrease in blood glucose levels. In conclusion, vascular smooth muscle proliferation is impaired by diabetes and stimulated by insulin treatment. Insulin-like growth factor I infusion stimulates vascular smooth muscle proliferation without affecting blood glucose, and gene expressions of insulin-like growth factor I and its receptor are increased in proliferating vascular smooth muscle, indicating that insulin-like growth factor I and involved in vascular smooth muscle proliferation in vivo.

Initial diabetic renal hypertrophy is preceded by a transient increase in kidney insulin-like growth factor I suggesting that insulin-like growth factor I may be implicated in diabetic kidney growth. The present study was undertaken to examine the effects of exogenous insulin-like growth factor I infusion on diabetic renal hypertrophy at a time when renal insulin-like growth factor I concentration had returned to normal and the initial steep kidney growth rate had diminished to a much slower rate. Groups of rats with diabetes duration of 5 days were infused s.c. for 4 subsequent days with equimolar concentrations of insulin-like growth factor I (36 nmol/day) or insulin (35 nmol/day). Insulin infusion lowered blood glucose to a normal level within 2 days and induced an average body-weight gain of 9.3 +/- 0.6 g/day. Insulin-like growth factor I infused diabetic rats maintained the original diabetic state with blood glucose levels comparable to those of 0.154 mol/l NaCl-infused diabetic rats, but had nevertheless an average body-weight gain of 6.8 +/- 1.0 g/day while untreated diabetic rats had a lower body-weight gain amounting to 3.3 +/- 0.8 g/day (p less than 0.01). The kidney weight at day 9 in untreated diabetic animals was about 25% greater than that of non-diabetic control animals, while in insulin-like growth factor I treated diabetic rats a further increase (p less than 0.05) was seen, amounting to 36% above control level. No increase was seen in the insulin-treated diabetic group.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding and growth promoting effects of insulin, insulin analogues modified in the B chain, proinsulin, insulin-like growth factor-I and -II were studied in cultured rat aortic smooth muscle cells. Specific binding of 125I-insulin was 0.9 +/- 0.2% of total 125I-insulin added, and the IC50-value was estimated to 8.9 pmol/l. The insulin analogue B10 Asp tended to be more potent than insulin in displacing 125I-insulin, B28 Asp was equipotent, B9 Asp/B27 Glu was approximately 100 times less potent and insulin-like growth factor-I more than 1000 times less potent than insulin. Specific binding of 125I-insulin-like growth factor-I after 4 h incubation at 10 degrees C was five times higher than the specific binding of insulin (4.4 +/- 0.4% of total 125I-insulin-like growth factor-I added), and the IC50-value was 0.3 nmol/l. Insulin was approximately 500 times less potent than insulin-like growth factor-I in displacing 125I-insulin-like growth factor-I. The insulin analogue B10 Asp was slightly more potent and analogue B28 Asp was equipotent with insulin. Analogue B9 Asp/B27 Glu was ten times less potent and proinsulin was more than ten times less potent than insulin. The order of potency was similar for 3H-thymidine incorporation into DNA: insulin-like growth factor-I greater than B10 Asp greater than insulin-like growth factor-II greater than insulin greater than or equal to B28 Asp greater than B9 Asp/B27 Glu greater than proinsulin. The maximal effect of insulin-like growth factor-I on 3H-thymidine incorporation was 71 +/- 16% higher than the maximal effect of insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

It has recently been demonstrated that immunoassayable kidney insulin-like growth factor I concentration increases 24-48 h after induction of diabetes, preceding the initial renal hypertrophy. To elucidate whether this increase is due to increased local production we studied rat kidney insulin-like growth factor I gene expression during the first four days after induction of streptozotocin diabetes. Eighteen hours after injection with streptozotocin the diabetic animals were divided into two groups, one of which was treated with insulin, and daily for four days animals from each group were taken out for investigation. After four days the wet kidney weight had increased from baseline by 20% (from 687 +/- 23 to 827 +/- 6 mg (mean +/- SEM), p less than 0.01) in the untreated diabetic group, while no significant increase occurred in the insulin-treated group (687 +/- 23 vs 732 +/- 21 mg, NS). Kidney insulin-like growth factor I increased rapidly from baseline, the rise amounting to 52% after 48 h (from 271 +/- 11 to 411 +/- 32 ng/g, p less than 0.01) with a decline to control level on day four in the untreated diabetic group. Kidney insulin-like growth factor I remained unchanged in the insulin-treated diabetic group. Insulin-like growth factor I mRNA was measured by solution-hybridization assay. No differences were found in kidney insulin-like growth factor I mRNA between the two diabetic groups over the study period, while in liver, insulin-like growth factor I mRNA tended to be lower on day four in diabetic rats when compared to insulin-treated rats (p = 0.07).(ABSTRACT TRUNCATED AT 250 WORDS)