Bioactive constituents of Corni Fructus: The therapeutic use of morroniside, loganin, and 7-O-galloyl-D-sedoheptulose as renoprotective agents in type 2 diabetes

Corni Fructus, the fruit of Cornus officinalis Sieb. et Zucc. (Cornaceae), is an important crude herb used in Chinese medicine to exhibit several biological activities, including hypoglycemic, antineoplastic, and antimicrobial effects, and to improve liver and kidney functions. We have been investigating the mechanism and bioactive constituents of Corni Fructus using diabetic animal models. Morroniside, loganin, and 7-O-galloyl-D-sedoheptulose, the main active compounds of Corni Fructus, exhibit the same lowering effects of elevated triglyceride, oxidative stress and advanced glycation endproduct (AGE) formation in the kidney of db/db mice. The effects of morroniside and 7-O-galloyl-D-sedoheptulose were mediated through modulation by renal sterol regulatory element binding proteins and nuclear factor-kappa B expression, but the effect of loganin was presumably mediated by hypoglycemic and antioxidant effects in the kidney, and also indirectly by the amelioration of metabolic disorders in other organs such as the liver. These findings led us to conclude that morroniside, loganin, and 7-O-galloyl-D-sedoheptulose would synergistically contribute to the inhibition of metabolic disorders (hyperglycemia and dyslipidemia), oxidative stress, inflammation, as well as AGE formation in the diabetic kidney.

REELIN and schizophrenia: a disease at the interface of the genome and the epigenome

The downregulation of the Reelin gene (RELN) that occurs in schizophrenic brains, which are characterized by pyramidal neurons with shortened dendrites and by reduced expression densities of dendritic spines, may well result from hypermethylation of the RELN promoter. In the adult mammalian brain, gamma-aminoburytic acid-secreting (GABAergic) interneurons release RELN into the extracellular matrix, where it binds with high affinity to the integrin receptors present at dendritic spine postsynaptic densities and likely plays a role, elaborated in this article, in synaptic plasticity. In heterozygous reeler mice, which are haploinsufficient in RELN, inhibitors of histone deacetylase increase DNA demethylase activity and restore RELN expression. Such inhibitors could thus be of therapeutic value in mitigating vulnerability to schizophrenia among high-risk individuals.

5-Hydroxytryptamine attenuates free radical injury in primary mouse cortical cultures

The effects of 5-hydroxytryptamine (5-HT) on several types of neuronal injury in mouse cortical cell cultures were tested. Co-treatment with 5-HT prevented free radical-mediated neuronal necrosis induced by FeCl2 or buthionine sulfoximine (BSO) in a dose-dependent manner. Subtype antagonists did not reverse the protective effect and 5-HT showed direct free radical scavenging activity evidenced by its ability to reduce the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) in a cell-free system. Excitotoxic necrosis induced by NMDA or apoptosis induced by staurosporine was not sensitive to 5-HT treatment. These features raise the possibility that the endogenous neurotransmitter 5-HT may work as an innate antioxidant defense mechanism in the CNS.

Haloperidol-induced neuronal apoptosis: role of p38 and c-Jun-NH(2)-terminal protein kinase

We examined patterns and mechanisms of cell death induced by haloperidol. Cortical cell cultures exposed to 10-100 microM: haloperidol for 24 h underwent neuronal death without injuring glia. The degenerating neurons showed hallmarks of apoptosis, featuring cell body shrinkage, nuclear chromatin condensation and aggregation, nuclear membrane disintegration with intact plasma membrane, and prominent internucleosomal DNA fragmentation. Neither glutamate antagonists nor antioxidants prevented the haloperidol-induced neuronal apoptosis. The c-Jun-NH(2)-terminal protein kinase and p38 mitogen-activated protein kinase were activated within 1 h and were sustained over the next 3 h following exposure of cortical neurons to 30 microM haloperidol. Haloperidol-induced neuronal apoptosis was partially attenuated by 10-30 microM PD169316, a selective inhibitor of p38 mitogen-activated protein kinase. Inclusion of 1 microg/ml cycloheximide, a protein synthesis inhibitor, or 100 ng/ml insulin prevented activation of both kinases and subsequent neuronal death. The present study demonstrates that cortical neurons exposed to haloperidol undergo apoptosis depending on activation of p38 mitogen-activated protein kinase and c-Jun-NH(2)-terminal protein kinase sensitive to cycloheximide and insulin.

Neurotoxic and neuroprotective actions of catecholamines in cortical neurons

We examined the possibility that catecholamines (CA) could act as endogenous modulators of neuronal death. Exposure to high doses (>100 microM) of dopamine (DA) caused widespread neuronal death within 24 h in mouse cortical cell cultures and was accompanied by cell body shrinkage, aggregation and condensation of nuclear chromatin, and prominent internucleosomal DNA fragmentation. Epinephrine, but not norepinephrine (NE), was slightly toxic to neurons at doses higher than 1 mM. DA-induced death was attenuated by the addition of three different anti-apoptosis agents, 1 microgram/ml cycloheximide, 25 mM K(+), or 100 ng/ml brain-derived neurotrophic factor (BDNF). While treatment with 100 microM N-acetyl-l-cysteine attenuated DA neurotoxicity, neither the glutamate antagonists (10 microM MK-801 plus 50 microM CNQX) nor several antioxidants [trolox, 100 microM; Mn (III) tetrakis (4-benzoic acid) porphyrin chloride, 100 microM; Mn (III) tetrakis (1-methyl-4-pyridyl) prophyrin pentachloride, 100 microM; N-tert-butyl-alpha-phenylnitrone, 3 mM] prevented the CA-induced apoptosis. Interestingly, all CA at 1-30 microM attenuated free radical-mediated neuronal necrosis following exposure to 30 microM Fe(2+) or 200 microM H(2)O(2), which was insensitive to DA or NE antagonists. Like trolox, CA reduced levels of the stable free radical 1,1-diphenyl-2-picrylhydrazyl under cell-free conditions, raising the possibility that CA as an antioxidant protects neurons. We also found that the neuroprotective effect of CA prolonged the protective effects of BDNF against serum deprivation. The present findings suggest that CA induces apoptosis at high doses but prevents free radical-mediated neurotoxicity as an anti-oxidant without being coupled to the receptors.

Phosphatidylinositol 3-kinase-mediated regulation of neuronal apoptosis and necrosis by insulin and IGF-I

We examined effects of two insulin-like growth factors, insulin and insulin-like growth factor-I (IGF-I), against apoptosis, excitotoxicity, and free radical neurotoxicity in cortical cell cultures. Like IGF-I, insulin attenuated serum deprivation-induced neuronal apoptosis in a dose-dependent manner at 10-100 ng/mL. The anti-apoptosis effect of insulin against serum deprivation disappeared by addition of a broad protein kinase inhibitor, staurosporine, but not by calphostin C, a selective protein kinase C inhibitor. Addition of PD98059, a mitogen-activated protein kinase kinase (MAPKK) inhibitor, blocked insulin-induced activation of extracellular signal-regulated protein kinases (ERK1/2) without altering the neuroprotective effect of insulin. Cortical neurons underwent activation of phosphatidylinositol (PI) 3-kinase as early as 1 min after exposure to insulin. Inclusion of wortmannin or LY294002, selective inhibitors of PI 3-K, reversed the insulin effect against apoptosis. In contrast to the anti-apoptosis effect, neither insulin nor IGF-I protected excitotoxic neuronal necrosis following continuous exposure to 15 microM N-methyl-D-aspartate or 40 microM kainate for 24 h. Surprisingly, concurrent inclusion of 50 ng/mL insulin or IGF-I aggravated free radical-induced neuronal necrosis over 24 h following continuous exposure to 10 microM Fe2+ or 100 microM buthionine sulfoximine. Wortmannin or LY294002 also reversed this potentiation effect of insulin. These results suggest that insulin-like growth factors act as anti-apoptosis factor and pro-oxidant depending upon the activation of PI 3-kinase.

Attenuation of oxidative neuronal necrosis by a dopamine D1 agonist in mouse cortical cell cultures

Events which lead to an increase in intracellular free radicals induce necrotic cell death of cultured cortical neurons. In the present study, we report that treatment with 1 microM (+/-)-SKF-38393 hydrochloride, a selective D1 agonist, as well as 100 microM trolox, a lipophilic vitamin E analogue, significantly prevented oxidative-related necrotic cell death following exposure to 10 microM Fe2+ or 1 mM buthionine sulfoximine, an inhibitor of gamma-glutamylcysteine synthetase. The neuroprotective effect of (+/-)-SKF-38393 hydrochloride was partially reversed by addition of (+/-)-SKF-83566 hydrochloride, a selective D1 antagonist. Quinelorane dihydrochloride, a selective D2 agonist, did not influence free radical neurotoxicity. Interestingly, inclusion of (+/-)-SKF-38393 hydrochloride or quinelorane dihydrochloride did not attenuate apoptotic cell death of cortical neurons deprived of serum. The present study provides evidence that (+/-)-SKF-38393 hydrochloride attenuates oxidative neuronal necrosis, which has unique therapeutic potential for the treatment of various neurodegenerative diseases linked to oxidative stress.