Boldine prevents diabetes-induced skeletal muscle dysfunction by inhibiting large-pore channels
BackgroundDiabetes mellitus leads to skeletal muscle dysfunction associated with loss of strength, impaired blood perfusion, lipid accumulation, and inflammation. The opening of large-pore channels has been linked to increased membrane permeability and inflammatory signaling in several pathologies. Boldine, an alkaloid from Peumus boldus, blocks large-pore channel activity and exhibits antioxidant and anti-inflammatory properties. This study evaluated whether boldine prevents skeletal muscle alterations induced by diabetes and explored potential underlying mechanisms. MethodsDiabetes was induced in male C57BL/6J mice using streptozotocin (STZ, 40 mg/kg/day for 5 days). Diabetic mice were treated with boldine (50 mg/kg/day) for four weeks. Muscle strength and resting membrane potential were analyzed in vivo. Also, right gastrocnemius muscle blood perfusion at basal and after acetylcholine (10 M) stimulation were analyzed in vivo. Lipid accumulation was assessed using Oil Red O staining, and CD31 immunodetection was used to evaluate capillary density. mRNA levels of NLRP3 were evaluated in muscle by qPCR. In human myoblasts (AB1167) cultured under low (8 mM) or high glucose (25 mM) conditions, with or without boldine, membrane permeability (ethidium uptake), intracellular Ca{superscript 2} (Fura-2), nitric oxide (DAF-FM), and levels of NLRP3 and Casp1 (qPCR) and reactivity PPAR{gamma} (Immunofluorescence) were determined. ResultsSTZ mice showed reduced muscle strength and depolarized resting membrane potential, both prevented by boldine. Basal muscle perfusion was [~]20% lower in diabetic mice (160.1 {+/-} 17.2 vs. 199.1 {+/-} 13.8 units), whereas boldine preserved perfusion (184.6 {+/-} 14.3 units). Oil Red O-positive fibers increased to 52.4 {+/-} 3.6% in diabetic mice and decreased to 15.2 {+/-} 4.1% with boldine (control: 3.1 {+/-} 1.3%; p<0.05). NLRP3 mRNA increased 17.7 {+/-} 2.8-fold in diabetic muscle and was reduced by [~]50% with boldine. In myoblasts, high glucose increased ethidium uptake, nitric oxide production, NLRP3 and caspase-1 expression, and nuclear PPAR{gamma} ([~]45% positive nuclei); all effects were prevented by boldine. ConclusionsBoldine preserves skeletal muscle function and vascular reactivity in diabetes and prevents lipid accumulation and inflammasome activation both in vivo and in vitro. These effects are associated with inhibition of large-pore channel activity and attenuation of downstream calcium-dependent, inflammatory, and adipogenic pathways, supporting boldine as a promising therapeutic candidate for diabetes-associated skeletal muscle dysfunction. Graphical abstractIn myoblasts, high glucose activates large-pore channels, elevating cytoplasmic Ca{superscript 2} concentration and nitric oxide generation, which increases the activity of Cx-formed hemichannels, raises the levels of inflammasome components, and promotes lipid accumulation. In STZ-diabetic mice, de novo expression of large-pore channels in skeletal muscles contributes to reduced blood perfusion, accumulation of intramuscular fat, muscle weakness, and reduced resting membrane potential of myofibers. Boldine inhibits large-pore channel activity, preventing these alterations and preserving muscle physiology in vivo. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/707704v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@19179b4org.highwire.dtl.DTLVardef@1cd3d21org.highwire.dtl.DTLVardef@16851d6org.highwire.dtl.DTLVardef@1d4e77c_HPS_FORMAT_FIGEXP M_FIG C_FIG