THE IMMUNOSUPPRESSANT DRUG FK506 AMELIORATES SECONDARY MITOCHONDRIAL DYSFUNCTION FOLLOWING TRANSIENT FOCAL CEREBRAL-ISCHEMIA IN THE RAT

Recirculation following 2 h of focal ischemia due to transient middle cerebral artery (MCA) occlusion has previously been found to be accomp anied by an initial, partial recovery of the cellular bioenergetic sta te and of mitochondrial respiratory functions, with secondary deterior ation during the first 2-4 h of reflow. Both the free radical spin tra p alpha-phenyl-N-tert-butyl nitrone (PBN) and the immunosuppressant dr ug FK506 ameliorate the damage incurred by the 2-h period of focal isc hemia, even when given 1-3 h after the start of the recirculation. The primary objective of this study was to find out if FK506, like PEN, p revents the secondary deterioration of mitochondrial function, as this can be studied in vitro. Since this proved to be the case, we address ed the question of whether the secondary mitochondrial dysfunction and bioenergetic failure were related to a secondary compromise of microc irculation and cellular oxygen delivery. Six groups of male Wistar rat s were studied for measurement of mitochondrial respiratory activity ( total, n = 36). One group was used as control (n = 6). In the other gr oups of animals, MCA occlusion of 2 h duration was induced by an intra luminal filament technique. Neocortical focal and perifocal (''penumbr a'') tissues were sampled after 2 h of ischemia (n = 6) and after 1 h (n = 6), 2 h (n = 6 with vehicle), and 4 h (n = 6 with vehicle; n = 6 with FK506) of recirculation. The vehicle or 1.0 mg . kg(-1) of FK506 was injected intravenously after 1 h of recirculation. Homogenates wer e prepared, and stimulated (+ADP), nonstimulated (-ADP), and uncoupled respiratory rates were measured polarographically. The uncoupling age nt used was carbonyl cyanide m-chlorophenylhydrazone, Local CBF and ti ssue oxygen tension were evaluated by laser-Doppler flowmetry and PO2 microelectrodes, respectively, throughout the whole periods of 2 h of ischemia and 4 h of recirculation, using a remote MCA occlusion techni que. After 2 h of ischemia, the penumbra showed a moderate decrease an d the focus a marked decrease in ADP-stimulated and uncoupled respirat ory rates, with a marked fall in the respiratory control ratio, define d as ADP-stimulated divided by nonstimulated respiration. Recirculatio n (1 h) brought about partial recovery, but continued reflow (2 and 4 h) was associated with a secondary deterioration of respiratory functi ons. The secondary deterioration was prevented by FK506. The results t hus confirm previous findings showing that secondary mitochondrial dys function occurs following transient focal cerebral ischemia and demons trate that FK506, like PEN, improves the in vitro performance of mitoc hondria in focal and penumbral areas. Following MCA occlusion, local C BF in a penumbral area and tissue PO2 in a focal area decreased to abo ut 30 and 5% of control, respectively. However, recirculation brought about rapid recovery of blood flow and oxygen delivery. During the who le 4-h period of recirculation, local CBF and tissue PO2 were maintain ed close to 100% and at about 160% of the preischemic level, respectiv ely. The results make it highly unlikely that the secondary bioenerget ic failure during recirculation Is due to a compromised microcirculati on. it follows that oxygen delivery is not rate-limiting for recovery events. Very likely FK506 (and PBN) acts at the cellular level to impr ove mitochondrial energy functions. (C) 1997 Academic Press.