PURPOSE: It is well established that experimental testicular torsion induces 
germ cell specific apoptosis. Annexin V (BD Pharmingentrade mark) binds 
phosphatidylserine that becomes exposed on the cell membrane in apoptotic cells. 
In vivo detection of apoptotic cells with fluorescently labeled annexin V is an 
emerging technique that we evaluated for detecting apoptotic germ cells in a 
mouse model of testicular torsion.
MATERIALS AND METHODS: Annexin V labeled with an indocyanine fluorophore 
(bisfunctional succinimidyl ester of cyanine 5.5) (Amersham, Little Chalfont, 
United Kingdom) was injected intravenously in mice 18 hours after the repair of 
unilateral 720-degree testicular torsion for 2 hours. Serial fluorescence images 
were obtained 21, 24, 28 and 42 hours after torsion repair. Relative fluorophore 
localization was visualized in vivo using an optical small animal imaging system 
mounted with a filter in near infrared light. Average fluorescence intensity in 
torsed and sham testes was quantified in images of testes in situ exposed 
through an abdominal incision and in ex vivo testes.
RESULTS: A significant increase in fluorescence intensity was found in images of 
torsed vs sham operated testes. This was seen in ex vivo, exposed and in vivo 
testes (215%, 250% and 161%, respectively, p <0.05). Bisfunctional succinimidyl 
ester of cyanine 5.5 conjugated to dehydrogenase, a protein with a size similar 
to that of annexin V, was used to assess for capillary leakage. It was also more 
localized to the torsed testis relative to its contralateral sham control 
whether exposed or ex vivo (174% and 176%, respectively).
CONCLUSIONS: To our knowledge this study demonstrates for the first time the 
possibility of in vivo near infrared fluorescence imaging of apoptotic germ 
cells after testicular torsion in mice. It shows important confounding factors 
that must be considered as this new imaging technique is developed for detecting 
apoptotic cells in vivo in testes or in any other organ.