Pyrroloquinoline Quinone (PQQ) Prevents Cognitive Deficit Caused by Oxidative Stress in Rats

Abstract

The effects of pyrroloquinoline quinone (PQQ) and coenzyme Q(10) (Co Q(10)), either alone or together, on the learning ability and memory function of rats were investigated. Rats fed a PQQ-supplemented diet showed better learning ability than rats fed a CoQ(10)-supplemented diet at the early stage of the Morris water maze test. The combination of both compounds resulted in no significant improvement in the learning ability compared with the supplementation of PQQ alone. At the late stage of the test, rats fed PQQ-, CoQ(10)- and PQQ + CoQ(10)-supplemented diets showed similar improved learning abilities. When all the groups were subjected to hyperoxia as oxidative stress for 48 h, rats fed the PQQ- and CoQ(10) supplemented diets showed better memory function than the control rats. The concurrent diet markedly improved the memory deficit of the rats caused by oxidative stress. Although the vitamin E-deficient rats fed PQQ or CoQ(10) improved their learning function even when subjected to hyperoxia, their memory function was maintained by PQQ rather than by CoQ(10) after the stress. These results suggest that PQQ is potentially effective for preventing neurodegeneration caused by oxidative stress, and that its effect is independent of either antioxidant's interaction with vitamin E.

Keywords: coenzyme Q10; cognitive deficit; oxidative stress; pyrroloquinoline quinone.

Figures

Fig. 1

Effects of PQQ, CoQ10 and their combination on learning function of rats in a Morris water maze. Swimming frequency, once a day for 15 days for each group. Learning ability, expressed as average rate of decrease in latency time (days 2–5, 6–10 and 11–15) to find hidden platform from their values in the first trial. Open column, control rats fed normal diet; black column, rats fed PQQ-supplemented diet; dotted column, rats fed CoQ10-supplemented diet; and slashed column, rats fed concurrent diet of both antioxidants. *p<0.05 versus normal control rats at early stage, **p<0.02 versus normal control at late stage; means ± SE, n = 9 for each group of rats.

Fig. 2

Changes in memory retention of control rats fed normal diet (closed circle), and rats fed PQQ-supplemented diet (closed square), CoQ10-supplemented diet (opened triangle), and concurrent diet of both antioxidants (opened circle). Each group was subjected to hyperoxia as oxidative stress for 48 h. The arrowhead shows the endpoint of hyperoxia, and -2 day shows the start point of such stress. *p<0.05 versus normal control rats, **p<0.01 versus normal control rats, #p<0.05 versus rats fed PQQ-supplemented diet; means ± SE, n = 9 for each group for rats.

Fig. 3

Effects of PQQ, CoQ10 and their combination on impairment of learning function of vitamin E-deficient rats. Swimming frequency, once a day for 15 days for each group. Solid circle, vitamin E-deficient rats; open circle, vitamin E-deficient rats fed PQQ-supplemented diet; open square, vitamin E-deficient rats fed CoQ10-supplemented diet; and triangle, vitamin E-deficient rats fed concurrent diet of both antioxidants. *p<0.001 versus vitamin E-deficient rats; means ± SE, n = 9 for each group of rats.

Fig. 4

Effects of PQQ, CoQ10 and its combination diets on memory deficit of vitamin E-deficient rats. Closed circle, vitamin E-deficient rats without hyperoxia; closed square, vitamin E-deficient rats subjected to hyperoxia; open circle, vitamin E-deficient rats fed PQQ-supplemented diet and subjected to hyperoxia; open triangle, vitamin E-deficient rats fed CoQ10-supplemented diet and subjected to hyperoxia; closed triangle, vitamin E-deficient rats fed the concurrent diets and subjected hyperoxia. *p<0.01, **p<0.05 versus the vitamin E-deficient rats; #p<0.005 versus rats fed CoQ10-supplemented diet. The arrowhead shows the endpoint of hyperoxia, and -2 day shows the start point of such stress; means ± SE, n = 9 for each group of rats. The arrowhead shows the endpoint of hyperoxia, and -2 day shows the start point of such stress; means ± SE, n = 9 for each group of rats.