Nordihydroguaiaretic acid elevates osteoblastic intracellular Ca2+

Area of Science:

• Biochemistry
• Cell Biology
• Pharmacology

Background:

• Nordihydroguaiaretic acid (NDGA) is a known lipoxygenase inhibitor.
• Emerging evidence suggests NDGA affects intracellular calcium ([Ca2+]i) through non-canonical mechanisms.
• Understanding these mechanisms is crucial for its use as a pharmacological tool.

Purpose of the Study:

• To investigate the effect of NDGA on Ca2+ signaling in MG63 osteoblastic cells.
• To elucidate the specific pathways involved in NDGA-induced intracellular calcium increases.
• To determine if NDGA's effects on calcium are related to its lipoxygenase inhibitory activity.

Main Methods:

• Utilized fura-2 as a calcium indicator to measure intracellular calcium levels in MG63 cells.
• Administered varying concentrations of NDGA and assessed concentration-dependent effects.
• Manipulated extracellular calcium levels and employed specific inhibitors (verapamil, diltiazem, nifedipine, nimodipine, nicardipine, thapsigargin, U73122) to probe calcium signaling pathways.
• Investigated the role of protein kinase C using phorbol 12-myristate 13-acetate and GF 109203X.

Main Results:

• NDGA induced a concentration-dependent increase in intracellular calcium ([Ca2+]i) in osteoblasts.
• The calcium signal involved both release from intracellular stores and influx from extracellular sources.
• NDGA's effect on [Ca2+]i was independent of lipoxygenase inhibition, phospholipase C activity, and protein kinase C modulation.
• NDGA-induced calcium release was partially sensitive to thapsigargin, an endoplasmic reticulum Ca2+ pump inhibitor.

Conclusions:

• NDGA elevates intracellular calcium ([Ca2+]i) in osteoblasts via lipoxygenase-independent mechanisms.
• The observed calcium increase results from the release of stored calcium and subsequent calcium influx.
• These findings highlight novel calcium-modulating actions of NDGA beyond its known pharmacological targets.