Recombinant human insulin-like growth factor-I (rhIGF-I) therapy in adults with type 1 diabetes mellitus: effects on IGFs, IGF-binding proteins, glucose levels and insulin treatment.

OBJECTIVE: Insulin-like growth factor-I (IGF-I) has both insulin-like and anabolic actions but unlike insulin, IGF-I circulates bound to a number of specific binding proteins that regulate its availability and activity. Patients with type 1 diabetes mellitus have low levels of circulating IGF-I despite increased growth hormone (GH) secretion, and are a group that may benefit from rhIGF-I therapy. Understanding the relationship between IGF-I and its binding proteins is necessary to appreciate the actions of exogenously administered rhIGF-I. Therefore, we examined the effects of 19 days' subcutaneous administration of rhIGF-I (50 micrograms/kg BID) on the levels of IGF-I, IGF-II and the IGF-binding proteins (IGFBPs), as well as the daily dose of insulin necessary to maintain glycaemic control in patients with type 1 diabetes mellitus. DESIGN AND PATIENTS: This was an open study, and the patients were studied initially while resident (days 1-5) in the hospital and thereafter (days 6-24) as outpatients. Serum was collected at baseline and at intervals throughout the study for the measurement of total IGF-I, IGF-II, IGFBP-1, -2, -3, free insulin and growth hormone (GH). Daily insulin doses and glucometer readings were recorded throughout the study. The changes in each of these variables were examined. The subjects were six adults (35.3 +/- 4.0 years, mean +/- SE), with type 1 diabetes, and all had reasonable glycaemic control (HbA1c 7.2 +/- 0.5%). RESULTS: rhIGF-I administration increased circulating total IGF-I over two-fold (15.3 +/- 1.9 vs. 33.7 +/- 5.4 nmol/l, mean +/- SEM, P < 0.01, day 1 vs. day 20) and decreased plasma IGF-II concentration (85.0 +/- 4.7 vs. 50.6 +/- 4.7 nmol/l, P < 0.01, day 1 vs. day 20). The dose of insulin required for adequate glycaemic control decreased significantly during rhIGF-I therapy (46 +/- 7 vs. 31 +/- 8 U/day, P < 0.05, day -1 vs. day 19), as did the fasting free insulin concentration (8.4 +/- 1.5 vs. 5.0 +/- 0.8 mU/l, P < 0.05, baseline vs. day 5). IGFBP-2 concentration increased (388 +/- 115 vs. 758 +/- 219 micrograms/l, P < 0.05, day 1 vs. day 20), but IGFBP-1 and IGFBP-3 were unchanged during rhIGF-I treatment. Mean nocturnal GH concentration decreased (12.7 +/- 3.3 vs. 3.8 +/- 0.9 mU/l, P = 0.05) after 4 days' rhIGF-I therapy. CONCLUSION: Twice daily rhIGF-I therapy in adults with type 1 diabetes resulted in an increase in circulating IGF-I with a reciprocal decrease in IGF-II, and a marked elevation of IGFBP-2 concentration. The levels of IGFBP-1 and -3 were not dramatically changed despite a reduction in the concentration of serum free insulin, and a large decrease in the requirement for insulin. The mechanisms behind these changes remains unclear but alterations in circulating levels of of IGFBPs may alter IGF-I bioactivity. If rhIGF-I is to have an application in the management of adults with type 1 diabetes, further work is necessary to determine the metabolic consequences of the alterations seen in the IGFs and their binding proteins following rhIGF-I administration.

Systemic administration of rhIGF-I enhanced regeneration after sciatic nerve crush in mice.

Despite numerous reports suggesting that insulin-like growth factor-I (IGF-I) may be involved in the survival and regeneration of damaged neurons in vitro and after local administration in vivo, there have been few studies on the effect of IGF-I administered systemically on regeneration of damaged nerves in vivo and the functional consequences of enhanced regeneration. In an earlier study, recombinant human IGF-I (rhIGF-I) administered systemically enhanced the rate of regeneration after a sciatic crush as measured by the number of nerve fibers/muscle section. The purpose of this study was to follow up this finding by evaluating whether rhIGF-I administered peripherally enhances the rate of functional recovery. In this study following nerve injury, mice lost the ability to grip a wire screen with their hind paws and to walk normally as indicated by a decrease in toe spread, internal toe spread and an increase in the angle between hind feet. The ability of injured mice treated with rhIGF-I to grip an inverted screen returned to control levels significantly faster than that of vehicle-treated mice (day 12 vs. day 15, respectively). Similarly, rhIGF-I treatment of injured mice resulted in toe spread, internal toe spread and angle values that were significantly better than that of vehicle-treated mice and returned to control levels faster than vehicle-treated injured mice. There was a parallel loss of innervation after sciatic nerve crush as measured by a loss in choline acetyltransferase activity in the soleus and gastrocnemius muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective down-regulation of D1 dopamine mediated rotational behavior in supersensitive mice.

The effects of continuous exposure to selective D1 and D2 agonists on rotational behavior were examined in mice with unilateral 6-hydroxydopamine-induced lesions of the corpus striatum. Continuously exposing mice to the D1 agonist SKF 38393 produced an initial rotational behavioral response which decreased dramatically within 4 hours. At the time these rotations ceased, the mice were totally unresponsive to an acute challenge injection of SKF 38393 but responded normally to an acute injection of the D2 agonist quinpirole. Mice chronically implanted with quinpirole also showed marked rotational behavior, but in contrast to the results with SKF 38393, essentially no diminution of these rotations was seen during a one week period of exposure. The results suggest that there are different mechanisms involved in the long term regulation of D1 and D2 dopamine systems in supersensitive animals.