Preptin

Preptin amplifies glucose-stimulated insulin secretion (GSIS) by acting on pancreatic beta cells via an autocrine/paracrine mechanism. It activates ERK1/2 signaling in beta cells, promoting their proliferation and enhancing Ca2+-dependent exocytosis of insulin granules. The net effect is a leftward shift in the glucose dose-response curve for insulin secretion, meaning beta cells secrete more insulin at any given glucose concentration in the presence of preptin.

Preptin binds osteoblast surface receptors and activates Wnt/beta-catenin and MAPK signaling, promoting osteoblast differentiation, matrix mineralization, and bone formation. It upregulates osteocalcin, collagen I, alkaline phosphatase, and Runx2 expression in osteoblast cultures. Preptin also indirectly reduces osteoclast activity by shifting the RANKL/OPG ratio toward OPG (osteoprotegerin), reducing bone resorption. The combined anabolic and anti-resorptive profile suggests net bone gain with preptin treatment.

Preptin administration in rodents reduces adiposity and increases lean body mass over time. These effects may be secondary to improved insulin sensitivity and enhanced glucose metabolism rather than direct adipose tissue effects. Preptin-treated cells show increased glucose oxidation and reduced lipid accumulation. Circulating preptin is reduced in postmenopausal women and in type 2 diabetes, correlating with bone loss and impaired insulin secretion in these groups.

In ovariectomized rats (menopause model), preptin administration prevented bone loss, increased BMD, and improved bone mechanical strength comparable to low-dose estrogen. In diabetic rodent models with bone fragility, preptin restored osteoblast function and bone formation markers. These data suggest preptin may be a bone anabolic agent without the growth-promoting risks associated with PTH analogues or the cardiovascular concerns of estrogen.

Serum preptin is reduced in type 2 diabetes, particularly in poorly controlled patients. The reduction correlates with impaired GSIS and reduced beta cell mass. Whether low preptin is a cause or consequence of beta cell dysfunction is unresolved. Preptin supplementation in diabetic mouse models improved glucose tolerance and beta cell insulin content, suggesting a therapeutic rationale.

Postmenopausal women show lower preptin levels than premenopausal controls, with preptin negatively correlating with bone resorption markers (CTx, NTx) and positively correlating with bone formation markers (osteocalcin, P1NP). This suggests preptin decline contributes to the estrogen-independent component of postmenopausal bone loss. Clinical trials of preptin for osteoporosis have not yet been conducted.