Tc-99m pyrophosphate imaging of poloxamer-treated electroporated skeletal muscle in an in vivo rat model

Abstract

Objective: This study investigates whether (99m)Tc pyrophosphate (PYP) imaging provides a quantitative non-invasive assessment of the extent of electroporation injury, and of the effect of poloxamer in vivo on electroporated skeletal muscle.

Methods: High-voltage electrical shock was used to produce electroporation injury in an anesthetized rat's hind limb. In each experiment, the injured limb was treated intravenously by either poloxamer-188, dextran, or saline, and subsequently imaged with (99m)Tc PYP. The radiotracer's temporal behavior among the experimental groups was compared using curve fitting of time-activity curves from the dynamic image data.

Results: The washout kinetics of (99m)Tc PYP changed in proportion to the electric current magnitude that produced electroporation. Also, (99m)Tc PYP washout from electroporated muscle differed between poloxamer-188 treatment and saline treatment. Finally, 10-kDa dextran treatment of electroporated muscle altered (99m)Tc PYP washout less than poloxamer-188 treatment.

Conclusions: Behavior of (99m)Tc PYP in electroporated muscle appears to be an indicator of the amount of electroporation injury. Compared to saline, intravenous polaxamer-188 treatment reduced the amount of (99m)Tc PYP uptake. Coupled to results showing poloxamer-188 seals ruptured cellular membranes, lessens the extent of electroporation injury and improves cell viability, (99m)Tc PYP imaging appears to be a useful in vivo monitoring tool for the extent of electroporation injury.

Fig. 1

Photograph of the experimental setup, showing the anesthetized animal and the small gamma camera. The anesthetic infusion pump is seen at left and a syringe coupled to the jugular catheter is in the foreground; a pumped-water heating pad maintains the animal’s body temperature.

Fig. 2

Typical posterior-view image of ^99mTc PYP in the hind limbs. The left limb was shocked with 1.85 A pulses and ^99mTc PYP was injected at 30 min post-shock. The left limb was imaged for 12 min at 105 min post-shock; the right limb was imaged for 12 min at 120 min post-shock. The muscle of the shocked limb (left) shows substantially more uptake than does the muscle of the unshocked limb (right). The white boxes illustrate the typical placement of ROIs over the muscle.

Fig. 3

TACs for ^99mTc PYP in saline-treated electroporated muscle vs. applied current. Saline was injected 10 min post-shock (dotted line) and radiotracer was injected 30 min post-shock (dashed line). Error bars represent S.E.M.

Fig. 4

TAC of ^99mTc PYP in unshocked muscle treated with 17 mg poloxamer-188. The TACs for unshocked saline-treated and 1.85 A-shocked saline-treated muscle are shown for comparison. Saline or polox-amer-188 was injected 10 min post-shock (dotted line) and radiotracer was injected 30 min post-shock (dashed line). Error bars represent S.E.M.

Fig. 5

TACs of ^99mTc PYP in poloxamer-188-treated electroporated muscle. TACs for unshocked saline-treated muscle and saline-treated muscle shocked at 1.85 A are shown for comparison. Therapeutic agent was injected 10 min post-shock (dotted line); radiotracer was injected 30 min post-shock (dashed line). Error bars represent S.E.M.

Fig. 6

TACs of ^99mTc PYP for 1.85 A-shocked electroporated muscle treated with 10 and 40 kDa dextran. TACs for unshocked saline-treated muscle and saline-treated muscle shocked at 1.85 A are shown for comparison. Therapeutic agent was injected 10 min post-shock (dotted line); radiotracer was injected 30 min post-shock (dashed line). Error bars represent S.E.M.

Fig. 7

Comparison of TACs for treatment with 17 mg poloxamer-188 and 17 mg 10 kDa dextran. The TACs for 1.85 A-shocked and unshocked muscle treated with saline are shown for comparison. Therapeutic agent was injected 10 min post-shock (dotted line); radiotracer was injected 30 min post-shock (dashed line). Error bars represent S.E.M.