Pioglitazone does not adequately control hyperinsulinemia but does increase serum adiponectin concentrations in equids with severe insulin dysregulation.

Overview

Pioglitazone, given orally in horses and related equids with severe insulin dysregulation, does not adequately lower high insulin levels but does increase beneficial adiponectin levels, especially when given twice daily.

Study Purpose and Design

• Purpose: To evaluate the effects of pioglitazone on insulin and adiponectin levels in equids with severe hyperinsulinemia, a condition associated with insulin dysregulation.
• Dosage groups: Two treatment regimens were tested:
  • PIO-SID: 2 mg/kg pioglitazone once daily (every 24 hours)
  • PIO-BID: 2 mg/kg pioglitazone twice daily (every 12 hours)
• Subjects: 17 client-owned equids exhibiting resting insulin > 100 µIU/mL, indicating severe hyperinsulinemia.
• Duration: 70-day treatment and monitoring period with rolling enrollment over 11 months.
• Measurements:
  • Basal insulin concentrations
  • Total and high-molecular-weight adiponectin levels
  • Plasma pioglitazone concentrations
  • Oral sugar tests (OST) on day 0 and day 28 to assess insulin response to sugar challenge
• Analysis: Mixed-effects linear regression to evaluate changes over time and between treatment groups.

Key Findings

• Insulin Control:
  • Resting insulin levels decreased slightly but equivocal in both groups; not statistically significant nor consistent.
  • OST insulin levels (reflecting insulin response to sugar intake) did not improve in either group, indicating pioglitazone did not improve dynamic insulin regulation.
  • Pioglitazone did not normalize resting hyperinsulinemia.
• Adiponectin Response:
  • High-molecular-weight (active form) adiponectin significantly increased in the twice-daily group (PIO-BID) over 70 days, from about 3.5 µg/mL to 15.0 µg/mL.
  • No significant adiponectin increase was observed in the once-daily group (PIO-SID).
• Pioglitazone Plasma Levels:
  • PIO-BID group plasma concentrations (about 740 ng/mL) exceeded the human therapeutic threshold of 617 ng/mL.
  • PIO-SID group plasma levels were lower and more variable (around 292 ng/mL).

Interpretation and Implications

• Pioglitazone was not effective as a stand-alone therapy to reduce or normalize insulin levels in equids with severe insulin dysregulation.
• Significant increases in high-molecular-weight adiponectin—an adipokine linked to improved insulin sensitivity and anti-inflammatory effects—were observed with higher plasma drug concentrations achieved via twice daily dosing.
• The lack of improvement in insulin response despite increased adiponectin indicates pioglitazone’s glucose metabolism benefits may be limited or require adjunct therapies in severely affected equids.
• The increase in adiponectin suggests a potential beneficial metabolic effect that warrants further studies, possibly exploring combined treatment protocols or longer-term outcomes.
• The pharmacokinetic data (plasma concentration measurements) helped confirm that the twice daily dosing regimen achieved plasma levels comparable to effective human dosing, suggesting species-specific dosage considerations.

Conclusion

• Pioglitazone administered orally to equids with severe insulin dysregulation fails to adequately control hyperinsulinemia.
• However, it does increase serum adiponectin concentrations significantly when administered twice daily at 2 mg/kg.
• This adiponectin increase could have potentially beneficial metabolic effects, although clinical benefits in insulin regulation were not demonstrated in this study.
• Continued research is needed to investigate pioglitazone’s role as part of multi-modal treatment strategies for equine metabolic syndrome and related insulin dysregulation conditions.