Main Research Findings

1) Deprenyl was shown to increase the life span and activity levels of superoxide dismutase and catalase in selective brain regions.

2) Deprenyl reduces delayed neuronal death of hippocampal pyramidal cells

 

 

Selected Data
1) The study completed by researchers Kitani et al was designed to investigate whether chronic administration of (-)-deprenyl, a selective monoamine oxidase-B (MAO-B) inhibitor, could prolong lifespan and enhance antioxidant defense mechanisms in the brains of Fischer-344 rats. The investigators combined a long-term survival study with a series of biochemical experiments measuring antioxidant enzyme activities in multiple brain regions. Their primary objectives were to determine whether deprenyl extended longevity in aging rats and whether treatment altered the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in a manner that could potentially explain the drug’s reported anti-aging effects [1].
The lifespan experiment utilized male Fischer-344 rats that began treatment at 18 months of age, representing middle-aged animals before the onset of advanced senescence. Rats were randomly assigned to either a deprenyl-treated group or a saline-treated control group. Each treatment arm consisted of 35 animals, pooled from three separate experimental cohorts containing 15, 10, and 10 rats, respectively. Experimental animals received subcutaneous injections of deprenyl at a dose of 0.5 mg/kg three times per week, whereas control animals received equivalent volumes of physiological saline using the same schedule. Animals were housed three per cage under conventional clean conditions identical to those used in the institute’s aging colony. Throughout the study, no interventions were performed other than monthly body weight measurements, and all animals were observed until natural death. This design allowed the investigators to compare average survival times and remaining life expectancy between treated and untreated animals while minimizing experimental manipulation.
Separate biochemical experiments examined the effects of deprenyl on antioxidant enzyme activities in rats of different ages and both sexes. Animals received deprenyl either by repeated subcutaneous injection or by continuous subcutaneous infusion using osmotic minipumps. Most experiments involved 21 consecutive days of treatment, although additional studies extended drug administration to four weeks in order to evaluate time-dependent changes in enzyme activity. Following completion of treatment, animals were euthanized by decapitation, and several brain regions were rapidly dissected on ice. These regions included the striatum, substantia nigra, frontal cortex, parietotemporal cortex, occipital cortex, hippocampus, and cerebellum. Liver tissue was also collected in selected experiments to determine whether the effects of deprenyl were specific to the central nervous system or occurred systemically. Tissue homogenates were prepared according to previously validated laboratory protocols for biochemical enzyme analysis [1].
The investigators quantified multiple antioxidant enzymes using established biochemical assays. Total superoxide dismutase (SOD) activity was measured using the Elstner and Heupel method based on inhibition of nitrite formation from hydroxylamine in the presence of superoxide-generating systems. Potassium cyanide was incorporated into the assay to distinguish copper-zinc SOD (Cu/Zn-SOD) from manganese-dependent SOD (Mn-SOD) by selectively inhibiting the cytosolic enzyme. Catalase (CAT) activity was measured using the spectrophotometric method developed by Beers and Sizer, whereas glutathione peroxidase (GSH-Px) activity was determined according to the Paglia and Valentine procedure. Both selenium-dependent and non-selenium-dependent forms of glutathione peroxidase were analyzed using different peroxide substrates to provide a comprehensive assessment of antioxidant capacity. These complementary assays enabled investigators to determine whether deprenyl selectively influenced particular antioxidant systems or produced generalized changes in oxidative defense mechanisms [1].
Additional experiments evaluated the influence of drug dosage, sex, age, and treatment duration on antioxidant enzyme responses. Male and female rats, both young and old, received multiple doses of deprenyl ranging from 0.1 to 2.0 mg/kg/day, allowing the investigators to identify optimal doses for enzyme induction in each experimental group. Time-course studies further examined antioxidant enzyme activities after one, two, three, and four weeks of continuous drug infusion to determine whether enzyme responses were sustained or changed with prolonged exposure. These experiments were designed to establish whether biological variables influenced the magnitude or direction of deprenyl’s antioxidant effects.
Statistical analyses were performed using one-way ANOVA to compare multiple experimental groups. When significant overall differences were detected, Scheffé’s post hoc test identified specific group differences. Comparisons involving only control and treatment groups employed two-tailed Student’s t-tests for independent samples, while survival data from the three experimental cohorts were pooled after confirming the absence of cohort effects. Statistical significance was defined as p < 0.05, providing a rigorous analytical framework for evaluating the effects of chronic deprenyl treatment on longevity and antioxidant enzyme activity [1].
2) The study by researchers Paterson et al was designed to determine whether (-)-deprenyl could reduce delayed neuronal death following transient cerebral ischemia by using a rat model of unilateral hypoxia-ischemia. Previous studies had demonstrated that (-)-deprenyl possesses neuroprotective and anti-apoptotic properties independent of its MAO-B inhibitory effects. Because delayed neuronal death after ischemia has been linked to apoptotic mechanisms, the investigators hypothesized that administration of (-)-deprenyl during the post-ischemic period might preserve vulnerable hippocampal neurons. The study therefore combined a well-established experimental model of cerebral ischemia with histological analyses to quantify neuronal survival and reactive astrocyte proliferation following treatment. Adult male Wistar rats weighing 250–270 g were housed under standardized laboratory conditions using a 12-hour light/dark cycle with unrestricted access to food and water. Animals were acclimated before experimentation to minimize environmental stress that might influence the neurological response to ischemia [2].
To produce unilateral cerebral ischemia, rats were anesthetized with 2% halothane delivered in a mixture of oxygen and nitrous oxide. During the first surgical procedure, the left common carotid artery was permanently ligated, after which the incision was closed and animals were allowed to recover for twenty-four hours. On the following day, transient hypoxia was induced by placing each animal in a chamber containing a gas mixture of 1% carbon monoxide, 30% oxygen, and nitrogen for 30 minutes. The gas was delivered at a controlled flow rate while animals remained conscious but mildly sedated. Following completion of the hypoxic exposure, rats rapidly recovered normal movement and behavior. Preliminary experiments confirmed that carotid artery ligation alone or hypoxia alone did not produce significant neuronal damage, demonstrating that the combination of unilateral carotid occlusion and systemic hypoxia was necessary to generate the delayed hippocampal injury characteristic of this model.
The principal treatment group received (-)-deprenyl at a dose of 0.25 mg/kg by subcutaneous injection, whereas control animals received equivalent volumes of physiological saline. In the initial experiment, treatment was administered immediately at the onset of carbon monoxide exposure and continued once daily until animals were sacrificed after 1, 7, or 14 days. Additional experiments evaluated the importance of treatment timing by administering the first dose 2 hours before ischemia, 1 hour after ischemia, or 4 hours after ischemia, while maintaining daily injections thereafter. A separate treatment-duration experiment examined whether continuous therapy was necessary by administering (-)-deprenyl beginning 1 hour after ischemia and continuing treatment for 1, 3, or 7 days before sacrifice. These experimental variations allowed investigators to determine the optimal therapeutic window and duration of drug administration required to maximize neuroprotection [2].
At the designated survival times, animals were deeply anesthetized with chloral hydrate and euthanized by transcardiac perfusion with 4% buffered formaldehyde. Brains were removed, post-fixed overnight, cryoprotected in sucrose, rapidly frozen, and stored before sectioning. Coronal brain sections measuring 7 μm and 14 μm were prepared through the dorsal hippocampus. Standard thionin staining was used to visualize surviving pyramidal neurons, while immunohistochemical staining for glial fibrillary acidic protein (GFAP) identified reactive astrocytes as an indicator of gliosis following injury.
Quantitative histological analyses focused on the CA1, CA3, and CA4 hippocampal regions, which exhibit differing susceptibility to ischemic injury. Surviving pyramidal neurons and GFAP-positive astrocytes were counted within both the ipsilateral and contralateral hippocampi using at least three separate tissue sections from each animal. All cell counting was performed by an observer blinded to treatment assignment to minimize bias. Animals exhibiting excessive ischemic damage involving the dentate gyrus, cerebral cortex, or CA2 region, or those failing to develop unilateral astrocytosis indicating an inadequate ischemic insult, were excluded from the study. Fewer than 20% of animals met these exclusion criteria [2].
Statistical analyses were performed using two-way and three-way ANOVA to evaluate the effects of treatment, time, and brain region on neuronal survival and astrocyte counts. Significant interactions were further examined using simple main-effects analyses or the Newman–Keuls multiple comparison test. This experimental design enabled investigators to assess not only whether (-)-deprenyl reduced delayed neuronal death, but also how treatment timing and duration influenced its neuroprotective efficacy across multiple hippocampal subregions [2].

 

Discussion
1) The study conducted by Kitani et al demonstrated that chronic treatment with (-)-deprenyl significantly prolonged lifespan in male Fischer-344 rats while selectively enhancing antioxidant enzyme activity in specific brain regions. In the longevity study, rats receiving 0.5 mg/kg of deprenyl by subcutaneous injection three times per week beginning at 18 months of age lived significantly longer than saline-treated controls. Mean lifespan increased from 876.7 ± 108.7 days in control animals to 926.3 ± 97.4 days in the deprenyl-treated group, representing a 5.6% increase in total lifespan. When survival was calculated from the onset of treatment at 18 months of age, average remaining lifespan increased by 15.0%, while animals surviving beyond 24 months exhibited an even greater 33.8% increase in remaining life expectancy. All three survival comparisons reached statistical significance. However, the longest-lived 10% of animals did not differ significantly between treatment groups, indicating that deprenyl primarily improved average survival rather than extending the absolute maximum lifespan. These findings confirmed that chronic deprenyl administration produced a reproducible longevity benefit in this strain of aging rats [1].
Biochemical analyses revealed that deprenyl markedly increased the activity of several antioxidant enzymes, although the effects depended on the specific enzyme, brain region, sex, age, and drug dosage. Initial experiments in young male rats treated with 2.0 mg/kg/day for 21 consecutive days demonstrated nearly a threefold increase in both Cu/Zn-SOD and Mn-SOD activities within the striatum. Catalase activity also increased significantly by approximately 60%, whereas neither the selenium-dependent nor the non-selenium-dependent forms of GSH-Px changed significantly. These findings indicated that deprenyl selectively enhanced certain antioxidant defense systems rather than producing a generalized increase in all antioxidant enzymes [1].

Figure 1: Changes in the enzyme activities of SOD and catalase
The investigators next examined whether these effects occurred throughout the brain or were restricted to selected regions. Continuous infusion studies showed that increases in antioxidant enzyme activity were region specific. Significant elevations in SOD activity were observed in the substantia nigra, striatum, frontal cortex, parietotemporal cortex, and occipital cortex, whereas hippocampus, cerebellum, and liver exhibited little or no response to treatment. Similar regional selectivity was observed for catalase activity, suggesting that deprenyl preferentially influenced brain areas rich in dopaminergic neurons rather than uniformly affecting all tissues. Because the substantia nigra and striatum are particularly vulnerable to oxidative damage and neurodegeneration, the authors proposed that enhanced antioxidant defenses in these regions might contribute to the drug’s neuroprotective and longevity-promoting properties.
A major finding of the study was that the response to deprenyl varied substantially according to sex and age. In young female rats, administration of the same 2.0 mg/kg/day dose that dramatically increased SOD activity in young males instead produced a marked decrease in enzyme activity, while old female rats showed essentially no change at that dose. Subsequent dose-response experiments demonstrated that these apparently contradictory findings reflected differences in the optimal dose rather than fundamentally different biological responses. Young female rats achieved maximal increases in SOD activity at approximately 0.2 mg/kg/day, nearly tenfold lower than the optimal dose for young males. Aging altered these optimal doses in opposite directions: old male rats responded best to 0.5 mg/kg/day, whereas old female rats required approximately 1.0 mg/kg/day. When doses exceeded the optimal range, antioxidant enzyme activity declined and could even fall below normal control values, demonstrating a biphasic dose-response relationship in which excessive dosing reduced the beneficial effects of deprenyl [1].
Time-course experiments further demonstrated that antioxidant enzyme induction developed progressively during treatment. SOD activity in the substantia nigra and striatum began to increase after approximately one week of continuous drug infusion and continued rising through the fourth week of treatment. Catalase activity, however, exhibited a delayed response, remaining unchanged during the first week before increasing after two weeks and reaching peak activity around the third week. In several brain regions, including the frontal and parietotemporal cortices, enzyme activity declined slightly after four weeks despite continued treatment, suggesting that prolonged exposure gradually reduced the stimulatory effect. These observations indicated that both the duration of treatment and dosing schedule influenced the magnitude of antioxidant enzyme induction.
Throughout the lifespan study, body weights remained nearly identical between deprenyl-treated and control animals, indicating that the observed longevity benefit could not be explained by reduced food intake or caloric restriction, the only well-established intervention known to extend rodent lifespan. Nevertheless, investigators noted that variability in body weight increased among aging control animals because of greater tumor burden and more pronounced age-related weight loss, whereas deprenyl-treated rats exhibited more stable body weights during late life. Collectively, the findings demonstrated that chronic deprenyl treatment significantly prolonged survival while selectively increasing SOD and catalase activities in vulnerable brain regions without altering glutathione peroxidase activity. The researchers concluded that these region-specific enhancements of endogenous antioxidant defenses may represent an important mechanism underlying deprenyl’s reported neuroprotective and life-extending effects, although they emphasized that the precise causal relationship between antioxidant enzyme induction and increased longevity remained to be established [1].
2) The study by Paterson et al demonstrated that (-)-deprenyl significantly reduced delayed neuronal death in the hippocampus following unilateral hypoxia-ischemia while exerting little influence on the initial acute neuronal injury. Preliminary experiments confirmed the validity of the experimental model by showing that carotid artery ligation alone or carbon monoxide exposure alone failed to produce measurable neuronal loss or astrocytosis. Furthermore, neuron and astrocyte counts in the contralateral hippocampus of ischemic animals were indistinguishable from those of untreated control animals, allowing the contralateral side to serve as an internal control for subsequent analyses [2].
In saline-treated animals, neuronal loss progressed in a time-dependent manner and differed among hippocampal regions. The CA1 and CA4 regions showed significant neuronal loss within 24 hours of ischemia, indicating an early component of injury. However, neuronal degeneration continued over the following two weeks, resulting in almost complete destruction of pyramidal neurons by day 14. The CA3 region exhibited greater initial resistance, with little neuronal loss detected during the first week, but approximately 50% of neurons were lost between days 7 and 14. These observations demonstrated that delayed neuronal death represented a major component of ischemic injury, particularly in the CA3 and CA4 regions. In parallel with neuronal degeneration, GFAP-positive astrocytes increased significantly at 7 and 14 days in all hippocampal regions, indicating progressive reactive gliosis after ischemic damage.
Daily administration of (-)-deprenyl produced substantial preservation of hippocampal neurons when treatment began at the onset of ischemia. The drug had no measurable effect on neuronal loss observed during the first 24 hours, suggesting that it did not prevent the immediate consequences of ischemic injury. However, by 14 days, marked neuroprotection was evident throughout the hippocampus. In saline-treated animals, neuronal survival averaged only 4% in the CA1 region, 43% in CA3, and 13% in CA4. In contrast, deprenyl-treated animals exhibited 42% neuronal survival in CA1, 95% survival in CA3, and 85% survival in CA4. When delayed neuronal loss occurring after the first day was calculated, (-)-deprenyl reduced delayed neuronal death by approximately 66% in CA1, 91% in CA3, and 96% in CA4. Despite this dramatic preservation of neurons, treatment did not significantly alter the increase in GFAP-positive astrocytes, indicating that reactive astrocytosis developed independently of neuronal rescue [2].

 

Figure 2: Changes in neuronal counts and the number of GFAP-positive cells in lesioned and control hippocampi following treatment with (-)-deprenyl.
The investigators also examined the importance of the timing of drug administration. Surprisingly, pretreatment with (-)-deprenyl 2 hours before ischemia failed to improve neuronal survival. In contrast, initiating therapy 1 hour after or 4 hours after the ischemic insult produced significant protection of CA1 neurons. These findings suggested that deprenyl acts during the post-ischemic period rather than preventing the initial ischemic injury itself. The delayed therapeutic window further implied that the drug modifies downstream cellular processes activated after reperfusion instead of directly blocking the primary mechanisms responsible for oxygen deprivation [2].
Treatment duration proved equally important for achieving maximal neuroprotection. Animals receiving deprenyl for only one day or three days after ischemia showed only modest preservation of neurons. The greatest neuroprotective effect occurred when daily treatment continued for the entire seven-day observation period, indicating that prolonged drug exposure was necessary to suppress the ongoing process of delayed neuronal degeneration. This finding supported the hypothesis that neuronal death develops progressively over several days following ischemia and that continuous pharmacological intervention is required to interrupt this process effectively.
Overall, the investigators concluded that (-)-deprenyl selectively inhibits the delayed phase of ischemia-induced neuronal death without affecting the initial acute injury. The observation that treatment remained effective when initiated after reperfusion, combined with the requirement for sustained administration, suggested that its neuroprotective effects were unlikely to result solely from irreversible MAO-B inhibition. Instead, the findings were considered most consistent with an anti-apoptotic mechanism, although the authors acknowledged that apoptosis was not directly measured in this study. They concluded that (-)-deprenyl represents a promising neuroprotective agent capable of substantially preserving hippocampal pyramidal neurons following transient cerebral ischemia and recommended further investigation to determine whether the rescued neurons remain permanently viable and whether inhibition of apoptosis is the primary mechanism underlying the observed protection [2].

 

Disclaimer

**LAB USE ONLY**
*This information is for educational purposes only and does not constitute medical advice. THE PRODUCTS DESCRIBED HEREIN ARE FOR RESEARCH USE ONLY. All clinical research must be conducted with oversight from the appropriate Institutional Review Board (IRB). All preclinical research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).

 

CItations

[1] Kitani K, Kanai S, Carrillo MC, Ivy GO. (-)Deprenyl increases the life span as well as activities of superoxide dismutase and catalase but not of glutathione peroxidase in selective brain regions in Fischer rats. Ann N Y Acad Sci. 1994;717:60-71. doi:10.1111/j.1749-6632.1994.tb12073.x

[2] Paterson IA, Barber AJ, Gelowitz DL, Voll C. (-)Deprenyl reduces delayed neuronal death of hippocampal pyramidal cells. Neurosci Biobehav Rev. 1997;21(2):181-186. doi:10.1016/s0149-7634(96)00008-5

 

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