Stimulation of creatine kinase activity in rat skeletal tissue in vivo and in vitro by protease-resistant variants of parathyroid hormone fragments

Abstract

We have reported that mid-region fragments of human parathyroid hormone (hPTH), exemplified by hPTH-(28-48), stimulated [3H]thymidine incorporation into DNA and increased the specific activity of the brain-type isoenzyme of creatine kinase (CK) in both skeletal-derived cell cultures (ROS 17/2.8 cells) and immature rat epiphyseal cartilage and diaphyseal bone, without stimulating cyclic AMP synthesis which is a prerequisite for bone resorption. In the present study, substitution of amino acids in hPTH-(28-48), which resulted in increased resistance to proteolysis, produced variants that stimulated skeletal systems at two orders of magnitude lower concentration than the wild-type fragment. We modified hPTH- (28-48)

hPTH‐fragments (53–84) and (28–48) antagonize the stimulation of calcium release and repression of alkaline phosphatase activity by hPTH‐(1–34) in vitro

“…This contrasts with the more typical dose-dependence of the PTH-(53-84) effect and seems to imply that the two peptides have different mechanisms of action. Interestingly both fragments induced ALP activity in isolation, demonstrating that they are not simply inert peptides that prevent the binding of hPTH-(1-34), which is also supported by other studies both in vivo and in vitro [4][5][6][7][8][9][10]. In this report we show that the fragments induced ALP activity at low concentrations, whereas PTH-(1-34) significantly repressed ALP activity at concentrations of 0.1-10 nM.…”

“…The small N-terminally truncated PTH-fragments have also been shown to elicit a number of biological effects on bone cells, frequently contrary to those of the intact N-terminal PTH peptides. The mid-regional fragment PTH-(28-48) augments cell proliferation in bone forming cells in vivo [4] and in vitro in chondrocytes [5] and osteoblasts [6,7]. It also induces alkaline phosphatase (ALP) activity and osteocalcin mRNA expression in osteoblast-like cells [8] and collagen II gene expression in chondrocytes [9].…”

Stimulatory effects of creatine on metabolic activity, differentiation and mineralization of primary osteoblast-like cells in monolayer and micromass cell cultures

“…During bone development, CK enzyme activity peaks in diaphyseal bone and cartilage in rats of peripubertal age . In bone, similar to cartilage, CK is also experimentally increased both in vitro and in vivo by insulin growth factor I ; by 1,25dihydroxyvitamin D 3 (Somjen et al, 1984a;Somjen et al, 1984b); by parathyroid hormone (PTH) (Somjen et al, 1985a;Somjen et al, 1985b;Somjen et al, 1987;Kaye et al, 1990); by protease-resistant variants of PTH (Somjen et al, 1995); by prostaglandin E 2 (Somjen et al, 1985a;Somjen et al, 1985b); by 17b-estradiol (Gray, 1989;Kaye et al, 1990). Furthermore, the stimulation of bone cell energy metabolism by 17b-estradiol and testosterone is sex specific (Somjen et al, 1991).…”