Simplified and efficient labeling of human platelets in plasma using indium-111-2-mercaptopyridine-N-oxide: preparation and evaluation.

The need for a gamma-emitting radioactive agent that will label platelets in plasma efficiently by a procedure that can be used uniformly in each laboratory is well recognized. A water soluble sodium salt of 2-Mercaptopyridine-N-oxide (Merc) was evaluated that quantitatively chelated 111ln at a pH range of 0.7 to 7.4, and allowed greater than 80% incorporation of 111ln in platelets in plasma. This was dependent on pH, Merc concentration, and platelet concentration. Platelets were labeled using either preformed [111ln]Merc or incubating platelets with 2.5 micrograms dry Merc first and then with 111ln. The latter method provided a simple kit procedure that labeled platelets with negligible alteration of in vitro aggregability. In dogs, labeled platelets had normal survival (7.5 days), 66 +/- 6.6% recovery, detected vascular thrombi (thrombi/blood = 59.4), and pulmonary emboli (PE/blood = 46.2) by scintigraphy. In the kit procedure, the use of Merc compared favorably to that of oxine and tropolone.

Evaluation of indium-111-2-mercaptopyridine-N-oxide for labeling leukocytes in plasma: a kit preparation.

Pure neutrophils, lymphocytes, and mixed leukocytes have been labeled in vitro with 111ln chelated to a nontoxic, water soluble agent 2-mercaptopyridine-N-oxide (Merc). Cells were labeled in isotonic salt-balanced medium with preformed [111ln] Merc (yield greater than 95%), or in 0.5 ml autologous plasma by incubation with dry Merc first and then with 111ln (yield 75%). The latter method facilitated a kit procedure that required 2 micrograms dry Merc when acid citrate dextrose was used as anticoagulant or 20 micrograms when heparin was used. Labeling efficiency was dependent on cell concentration and pH. Labeled cells accumulated avidly in experimental abscesses and provided abscess/blood ratios of greater than 75 at 24 hr postinjection. In dogs, the liver uptake of labeled cells was only 18.8 +/- 7.1% compared to that of 48.5% when cells were labeled with [111ln]oxine.