Differential effects of insulin-like growth factor binding proteins-1, -2, -3, and -6 on cultured growth plate chondrocytes

Differential effects of insulin-like growth factor binding proteins-1, -2, -3, and -6 on cultured growth plate chondrocytes.BackgroundIn children with chronic renal failure (CRF), impairment of longitudinal growth is in part due to excess amounts of circulating high-affinity insulin-like growth factor binding proteins (IGFBPs) that might decrease or prevent insulin-like growth factor (IGF) binding to its signaling receptor. However, it appears from the clinical studies that various IGFBPs may have contrasting effects on longitudinal growth. Because of the potential importance of the IGFBPs as modulators of longitudinal growth in pediatric CRF, the aim of the present study was to investigate the biological effects of IGFBP-1, -2, -3, and -6 on cultured growth plate chondrocytes that express the type 1 IGF receptor.MethodsThe effects of exogenous IGFBPs on IGF-independent and IGF-dependent proliferation of rat growth plate chondrocytes in primary culture were investigated. Proliferation was assessed by colony formation of agarose-stabilized long-term suspension cultures and by the [3H]thymidine assay. The effects of IGFBPs on IGF-I binding and the binding of IGFBPs to chondrocytes were assessed by binding studies with radiolabeled proteins in monolayer culture.ResultsIntact IGFBP-1, IGFBP-2 and IGFBP-6 inhibited in equimolar concentration the IGF-I- and IGF-II-stimulated DNA synthesis and cell proliferation, whereas the biological activity of IGFBP-3 was complex. It had an IGF-independent antiproliferative effect and also inhibited IGF-dependent chondrocyte proliferation under coincubation conditions, whereas under preincubation conditions IGFBP-3 enhanced IGF-I-responsiveness. Studies on the mechanism by which IGFBP-3 potentiated IGF activity demonstrated that under preincubation conditions IGFBP-3 is capable to associate with the cell membrane and to facilitate IGF-I cell surface binding.ConclusionsIntact IGFBP-1, IGFBP-2 and IGFBP-6 act exclusively as growth inhibitors on IGF-dependent proliferation of growth plate chondrocytes. IGFBP-3, however, can either inhibit IGF-independent and IGF-dependent cell proliferation, or enhance IGF responsiveness of chondrocytes dependent on the temporal relationship to the IGF exposure

Growth hormone prevents steroid-induced growth depression in health and uremia

Growth hormone prevents steroid-induced growth depression in health and uremia. Treatment with supraphysiological doses of corticosteroids results in protein wasting and impairment of growth, whereas exogenous growth hormone (GH) causes anabolism and improvement of growth. We wanted to know whether the growth depressing effects of methylprednisolone (MP) are more expressed in an organism which is chronically diseased and whether these effects can be counterbalanced by concomitant treatment with recombinant human growth hormone (rhGH). MP in doses from 1 to 9 mg/kg/day caused a dose dependent reduction of length gain, weight gain and weight gain/food intake ratio in 140 g healthy female Sprague-Dawley rats. Food intake was not affected by MP. This points to a change in food metabolism as a mechanism for growth impairment. In addition, treatment with MP inhibited endogenous GH secretion, documented by serum GH concentration profiles over seven hours, decreased IGF-1 serum concentration and disturbed growth cartilage plate architecture. Concomitant treatment with 2.5 to 20 IU/rhGH/kg/day prevented the negative effects of MP on growth in a dose dependent manner and normallized growth plate architecture. In uremic rats in which food efficiency and growth was already reduced, 6 mg MP/kg/day further decreased length gain and prevented weight gain completely by bringing the weight gain/food conversion ratio to the nadir. All effects of MP including reduction of muscle mass could be prevented by concomitant treatment with 10 IU rhGH/kg/day. The effects of MP and rhGH on food efficiency and growth in uremic animals were numerically nearly identical to those in pair fed and ad libitum fed controls, but this may be more relevant in the diseased organism in which basal growth is already suppressed

Growth promoting effects of growth hormone and IGF-I are additive in experimental uremia.

Exogenous growth hormone (GH) stimulates the endogenous production of IGF-I and improves growth in uremia. We investigated whether exogenous IGF-I is also able to improve uremic growth failure in rats and whether the growth promoting effects of GH and IGF-I are additive. In female 150 g uremic (subtotal nephrectomy, NX) Sprague-Dawley rats, both rhGH in doses from 2 X 1.25 to 2 X 10 IU/kg bid s.c. and rhIGF-I in doses from 2 X 0.5 to 2 X 4.0 mg/kg bid s.c. caused a dose-dependent increase in weight gain and length gain. However, endogenous production of GH was suppressed by both agents. Peptide hormone treatment did not affect cumulative food intake, but significantly increased food efficiency ratio (weight gain/food intake). Concomitant s.c. treatment with maximally effective doses of rhGH (12 X 5 IU/kg bid) and of rhIGF-I (2 X 2 mg/kg bid) resulted in additive growth promoting effects in NX and pair-fed control (CO) animals during the observation period of 12 days. Cumulative length gain was 3.2 +/- 0.5 cm in solvent-treated NX-animals, 4.1 +/- 0.5 cm with rhGH (+ 28% above solvent), 4.2 +/- 0.6 cm with rhIGF-I (+ 31%) and 4.9 +/- 0.5 cm with both peptides (+ 53%). The food efficiency ratio was 0.16 +/- 0.05 in solvent NX, 0.33 +/- 0.04 with rhGH (+ 106% above solvent), 0.23 +/- 0.02 with rhIGF-I (+ 44%), and 0.38 +/- 0.02 with both peptides (+ 138%). Histomorphometric analysis and measurements of length gain by fluorescence microscopy in the upper tibial metaphysis confirmed the growth promoting effects of both peptide hormones. The serum concentrations of IGF binding protein (BP)-4 (Western ligand blotting analysis) and of IGFBP-2 (immunoblot) were increased in uremic animals whereas IGFBP-3 was unchanged. Treatment with IGF-I and/or rhGH increased serum concentration of IGF-I but did not change the IGFBP pattern. rhIGF-I lowered blood glucose levels within one to two hours after injection. The effect was most pronounced during the first treatment day and declined thereafter. Concomitant treatment with rhGH attenuated the glucose lowering effect of rhIGF-I (glucose serum concentration at day one: 120 +/- 11 mg% in solvent NX, 50 +/- 21 mg% with rhIGF-I, 80 +/- 24 mg% with both peptides). It is concluded that: (i) IGF-I is able to stimulate growth in NX animals but suppresses endogenous GH production in the long run; (ii) the concomitant treatment with IGF-I and GH has additive effects on growth; and (iii) concomitant treatment with rhGH prevents hypoglycemia that is noted with rhIGF-I alone

Salt restriction in kidney disease—a missed therapeutic opportunity?

The importance of salt restriction in the treatment of patients with renal disease has remained highly controversial. In the following we marshal the current evidence that salt plays a definite role in the genesis of hypertension and target organ damage, point to practical problems of salt restriction, and report on novel pathomechanisms of how salt affects blood pressure and causes target organ damage