Indoxyl sulfate induces skeletal resistance to parathyroid hormone in cultured osteoblastic cells

Area of Science:

• Nephrology
• Endocrinology
• Bone Biology

Background:

• Skeletal resistance to parathyroid hormone (PTH) is a known complication in chronic renal failure patients, but its underlying mechanisms remain unclear.
• Previous studies in renal failure animal models showed reduced PTH receptor (PTHR) expression alongside renal dysfunction.

Purpose of the Study:

• To investigate the role of indoxyl sulfate (IS), a prevalent uremic toxin (UTx), in mediating skeletal resistance to PTH.
• To determine if IS affects osteoblast function, PTHR expression, and oxidative stress in vitro.

Main Methods:

• Primary osteoblast cultures were established from mouse calvariae.
• Cells were cultured with varying concentrations of IS.
• Assays were performed to measure intracellular cyclic adenosine 3',5' monophosphate (cAMP) production, PTHR expression, and free radical production.
• Expression of organic anion transporter-3 (OAT-3) was assessed.

Main Results:

• Indoxyl sulfate (IS) suppressed PTH-stimulated cAMP production in osteoblasts.
• IS significantly decreased PTHR expression in a dose-dependent manner.
• IS exposure led to increased free radical production in osteoblasts, indicating augmented oxidative stress.
• Organic anion transporter-3 (OAT-3), responsible for IS uptake, was found to be expressed in osteoblasts.

Conclusions:

• Indoxyl sulfate (IS) impairs osteoblast function by augmenting oxidative stress and downregulating PTH receptor (PTHR) expression.
• Osteoblasts can uptake IS via OAT-3, suggesting a direct cellular mechanism for IS toxicity.
• Accumulated IS in renal failure contributes to skeletal resistance to PTH, highlighting a potential therapeutic target.