Cytochrome b(5) plays a key role in human microsomal chromium(VI) reduction

The reduction of chromium(VI) to Cr(III) results in the formation of reactive intermediates that contribute to the cytotoxicity, genotoxicity, and carcinogenicity of Cr(VI)-containing compounds. Previous studies suggest that human microsomal Cr(VI) reduction likely proceeds through cytochrome b(5). In order to better understand Cr(VI) toxicity in humans, the role of cytochrome b(5) in combination with P450 reductase was examined in the reductive transformation of Cr(VI). Proteoliposomes containing human recombinant cytochrome b(5) and P450 reductase were constructed. The ability of P450 reductase to mediate efficient electron transfer from NADPH to cytochrome b(5) was confirmed by spectral analysis. The NADPH-dependent Cr(VI) reduction rate mediated by proteoliposomes was then compared to that of human microsomes. When these rates were normalized to equivalent cytochrome b(5) concentrations, the NADPH-dependent Cr(VI) reduction rates mediated by human microsomes were essentially identical to those for proteoliposomes containing cytochrome b(5) plus P450 reductase. Proteoliposomes containing only P450 reductase or cytochrome b(5) exhibited poor Cr(VI) reducing capabilities. Since it had been previously shown that trace amounts of iron (Fe) could dramatically stimulate microsomal Cr(VI) reduction, the ability of Fe to stimulate Cr(VI) reduction by proteoliposomes was examined. Both ferric chloride (FeCl(3)) and ferric adenosine-5'-diphosphate (FeADP) were shown to stimulate Cr(VI) reduction; this stimulation could be abolished by the addition of deferoxamine, a specific Fe(III) chelator. The NADPH-dependent reduction rates of various ferric complexes by proteoliposomes were sufficient to account for the increased Cr(VI) reduction rates seen with the addition of FeCl(3) or FeADP. Cr(V) was detected by electron paramagnetic resonance (EPR) spectroscopy as a transient intermediate formed during NADPH-dependent Cr(VI) reduction mediated by proteoliposomes containing cytochrome b(5) and P450 reductase. Overall, cytochrome b(5) in combination with P450 reductase can account for the majority of the NADPH-dependent Cr(VI) reduction seen with human microsomes.     

Antiinflammatory properties of Hypoxis hemerocallidea corm (African potato) extracts in rats

The effects of aqueous and methanolic extracts of Hypoxis hemerocallidea corm, locally known as 'African potato' in South Africa, were examined on rat paw edema induced by subplantar injections of fresh egg albumin (0.5 ml/kg). Acetyl salicylic acid (100 mg/kg p.o.) was used as the reference antiinflammatory agent for comparison. Both the aqueous and methanolic extracts of H. hemerocallidea corm (500 mg/kg p.o.) progressively reduced rat paw edema induced by the subplantar injections of fresh egg albumin. The methanolic extract produced relatively greater and more pronounced antiinflammatory effect than the aqueous extract in the experimental animal model used. However, the two extracts of African potato examined in this study were found to be less potent than acetyl salicylic acid (ASA) as an antiinflammatory agent.     

Tissue Angiotensin-converting enzyme activity plays an important role in pressure overload-induced cardiac fibrosis in rats

It has been widely assumed that the cardiac angiotensin-generating system plays an important role in the development and maintenance of cardiac remodeling caused by pressure overload. The roles of angiotensin-converting enzyme (ACE) in pressure overload-induced cardiac hypertrophy and fibrosis in rats were investigated. Pressure overload was achieved by constricting the abdominal aorta above the renal arteries. After they underwent surgery, the rats were treated with a low or high dose of the ACE inhibitor imidapril (0.07 and 0.7 mg/kg/d s.c.) with an osmotic pump for 4 weeks. High-dose imidapril prevented the increase in blood pressure, cardiac hypertrophy, and fibrosis. Low-dose imidapril inhibited only cardiac fibrosis. ACE activity in the myocardium, but not in serum, was significantly increased in the rats with the banded aorta, and ACE immunoreactivity was increased in the areas of fibrosis. These changes were markedly reduced by both doses of imidapril. These results suggest that the increased local ACE expression contributes to the development of pressure overload-induced cardiac fibrosis but is not responsible for hypertrophy in rats.     

Further observations on the role of -aminobutyric acid in insulin-induced hypoglycaemic convulsions

Drugs that increase brain γ-aminobutyric acid (GABA) or are essential for its metabolism affected the convulsions and reduction in the concentration of GABA in the cerebral hemispheres produced by insulin but not the hypoglycaemia. Hydroxylamine, mesantoin, caffeine and pyridoxine reduced insulin-induced convulsions while amino-oxyacetic acid completely suppressed them. These drugs increased significantly the insulin-depleted GABA concentration in the cerebral hemispheres of mice. Hydroxylamine, mesantoin and pyridoxine restored the concentrations of GABA to normal, while amino-oxyacetic acid and caffeine significantly increased the concentrations above normal. The results point to a probable role of GABA in insulin convulsions. They also indicate that the convulsant action of insulin in mice is not wholly explained by its ability to lower brain GABA levels.     

Involvement of nitric oxide (NO) in hypoglycaemic activity of tolbutamide

The study was conducted to find the involvement of Nitric Oxide (NO) using L-arginine, a NO precursor and NG-methyl L-arginine a nitric oxide synthase inhibitor on tolbutamide activity in normal rabbits. L-arginine (25-300 mg/kg, body weight, oral) produced transient and dose dependent hypoglycaemia. When combined with tolbutamide (40 mg/kg, oral) it produced early and prolonged action. The effect of tolbutamide was blocked by NG-methyl L-arginine (5 mg/kg, body weight, oral). The results confirm the involvement of NO in tolbutamide activity and the possibility of using L-arginine as a supplement to antidiabetic drugs in blood glucose control.     

Metabolic fate of the oral hypoglycaemic agent, midaglizole, in rats

1. The metabolic fate of midaglizole, 2-[2-(4,5-dihydro-1H-imidazole-2-yl)-1-phenylethyl]pyridine dihydrochloride sesquihydrate, was studied in rats after a single oral dose of 10 mg/kg. 2. After oral administration of 14C-midaglizole to rats, 63% of the dose was excreted in the urine and 41% in the faeces within 72 h. The major radioactive compound in the urine was unchanged midaglizole and accounted for 38.1% of the dose. In the faeces, two major radioactive compounds, M-VII and unchanged midaglizole, were present. These accounted for 17.2 and 14.1% of the dose, respectively. M-VII is a new metabolite, identified as 2-[2-(4,5-dihydro-1H-imidazole-2-yl)-1-(4-hydroxyphenyl)ethyl]pyridine by n.m.r. and mass spectrometry. 3. The biliary excretion of the radioactivity after oral administration of 14C-midaglizole to bile-duct cannulated rats amounted to 53% of the dose. Of the total amount of radioactivity excreted in the bile, 48% was calculated to be subject to enterohepatic recycling. 4. Four biliary metabolites were new metabolites and were identified by n.m.r., mass spectrometry and enzymic hydrolysis. These compounds are 2-[2-(4,5-dihydro-1H-imidazole-2-yl)-1-(4-hydroxyphenyl)-ethyl]pyridine O-glucuronide (M-XI), 2-[2-(4-hydroxyphenyl)-2-(2-pyridyl)]ethyl-2-imidazole O-glucuronide (M-XII),3-(4-hydroxyphenyl)-3-(2-pyridyl)propioimidamide O-glucuronide (M-XIII) and 2-[2-(4,5-dihydro-1H-imidazole-2-yl)-1-(4-hydroxy- 3-methoxyphenyl)ethyl]pyridine O-glucuronide (M-XIV). These glucuronides accounted for 35.4% of the dose. 5. Midaglizole was metabolized in rats mainly via phenyl ring para-hydroxylation followed by glucuronidation, with or without the biotransformation of the imidazoline ring moiety.     

Curative treatment with extracts of Bombax ceiba fruit reduces risk of calcium oxalate urolithiasis in rats

Context: Drawbacks of presently available treatments for urolithiasis necessitate finding the treatment of hyperoxaluria specifically aimed at reduction in oxalate excretion. Interestingly, many Indian tribes use Bombax ceiba L. (Bombacaceae) fruits as a traditional medicine for the treatment of urinary stones.

Objective: The present study investigated the efficacy of B. ceiba fruit extracts as curative agents in experimentally induced calcium oxalate urolithiatic rats.

Materials and methods: Calcium oxalate lithiasis was induced in rats by oral administration of 0.75% ethylene glycol for 14 consecutive days. Treatments with aqueous and ethanol extract of B. ceiba fruit (400?mg/kg body weight) was performed in the same manner for further 14 consecutive days. Cystone (750?mg/kg body weight) was used as reference antiurolithiatic drug. The urinary excretion and kidney deposition of offending salt components, and serum biochemical parameters were investigated.

Results: Oral administration of ethylene glycol resulted in hyperoxaluria and increased renal excretion of calcium and phosphate. However, supplementation with aqueous and ethanol extracts of B. ceiba fruit significantly (p?<?0.05) reduced the elevated urinary oxalate, showing a regulatory action on endogenous oxalate synthesis. The increased deposition of stone forming constituents in kidneys of calculogenic rats was also significantly lowered with curative treatment of aqueous and ethanol extract.

Discussion and conclusion: The results indicate that the fruit of B. ceiba is endowed with lithontriptic activity warranting further development for curative treatment of urolithiasis.     

The role of oxalate in star fruit neurotoxicity of five-sixths nephrectomized rats.

To investigate the role of oxalate in star fruit neurotoxicity, rats were given star fruit or oxalate after a sham operation or modified five-sixths nephrectomy; namely, star fruit (SC) or oxalate (OxC) for sham-operated rats and star fruit (SNx), calcium gluconate treated star fruit juice (SCaNx), or oxalate (OxNx) for nephrectomized rats. After feedings, none of the rats in SC, OxC, and SCaNx groups developed movement disorders or died, while all rats in SNx group and OxNx group presented movement disorders and two rats in SNx group and four rats in OxNx group died within minute to hour after development of myoclonic jerk and/or tonic-clonic convulsion. The plasma oxalate levels rose significantly only in the SNx group and OxNx group that also presented clusters of generalized spike-waves in the electroencephalographic recordings. In conclusion, oxalate may play a key role in star fruit neurotoxicity in nephrectomized rats and probably in uremic patients.     

Modulation of AT-1R/AMPK-MAPK cascade plays crucial role for the pathogenesis of diabetic cardiomyopathy in transgenic type 2 diabetic (Spontaneous Diabetic Torii) rats

There are evidences that the activation of AMPK is playing pivotal role in the lipid and glucose metabolism. It has been reported that both the AMPK and angiotensin-II acts as a negative regulator for each protein. It has been well proven that the MAPK cascade could be modulated by the presence of angiotensin-II. Moreover, studies were shown that p38 MAPK stimulates glucose uptake through the AMPK activation. Therefore, we speculate and tried to demonstrate that the modulation of AT-R/MAPK pathway through AMPK might play crucial roles for the pathogenesis of diabetic cardiomyopathy, using the transgenic (Spontaneous Diabetic Torii-SDT) rats. We performed Western blot analysis for the measurement of myocardial AT-R, AMPK and MAPK cascades-related protein expressions, p67-phox and caspase-12. In addition, we employed dihydroethidium (DHE), Azan Mallory and hemotoxylin eosin (HE) staining methods to demonstrate the superoxide radical production, fibrosis and hypertrophy, respectively. The protein expressions, such as AT-1R, p-ERK1/2, p67-phox and caspase-12 were found to be significantly increased and conversely, the Ang-(1-7) mas R, Tak1, LKB1 and p-AMPKα1, p-p38 MAPK and p-JNK protein expressions were found to be considerably decreased in the SDT rats, in comparison to the normal rats. The DHE, Azan Mallory and HE stainings also revealed that the SDT rats have more superoxide radical production, fibrosis and hypertrophy, respectively than the normal rats. Taken together, it is suggested that the modulation of AT-1R/AMPK-MAPK pathway might play crucial roles for the pathogenesis of diabetic cardiomyopathy and it could become an important therapeutic target to ameliorate the diabetic cardiomyopathy.     

Laboratory evaluation of the hypoglycemic effect of Anacardium occidentale Linn (Anacardiaceae) stem-bark extracts in rats

This study evaluated the hypoglycemic effect of stem-bark extracts of Anacardium occidentale Linn., of the Anacardiaceae family, in normal (normoglycemic) and in streptozotocin-treated diabetic rats. Young adult, male Wistar rats weighing 250-300 g were used. Diabetes mellitus was induced in the test rats by intraperitoneal injections of streptozotocin (STZ, 90 mg/kg). In one set of experiments, graded doses of the aqueous and methanolic stem-bark extracts of A. occidentale (100-800 mg/kg p.o.) were separately administered to groups of fasted normal and fasted diabetic rats. In another set of experiments, 800 mg/kg p.o. of the aqueous or methanolic extract of the plant, a dose which produced maximal hypoglycemic effects in both fasted normal and diabetic rats in the previous set of experiments, were used. The hypoglycemic effects of single doses (i.e., 800 mg/kg p.o.) of A. occidentale stem-bark aqueous and methanolic extracts were compared with those of insulin (5 microU/kg s.c.) and glibenclamide (0.2 mg/kg p.o.) in both fasted normal and fasted diabetic rats. Following acute treatment, relatively moderate-to-high doses of A. occidentale stem-bark extracts (100-800 mg/kg p.o.) produced dose-dependent, significant reductions (p< 0.05-0.001) in the blood glucose concentrations of both fasted normal and fasted diabetic rats. On their own, both insulin (5 microU/kg s.c.) and glibenclamide (0.2 mg/kg p.o.) produced significant reductions (p< 0.01-0.001) in the blood glucose concentrations of the fasted normal and fasted diabetic rats. At single doses of 800 mg/kg p.o., A. occidentale stem-bark aqueous and methanolic extracts significantly reduced (p< 0.001) the mean basal blood glucose concentrations of fasted normal and fasted diabetic rats. The hypoglycemic effect of the methanolic plant extract was found to be slightly more pronounced than that of the aqueous plant extract in both the normal and diabetic rats examined. A. occidentale contains a diverse group of chemical compounds. Since methanol extractives of plants usually contain many chemical compounds, each of which is capable of producing definite biological activities via different mechanisms, it is difficult to draw any logical conclusion on the mechanism of the hypoglycemic effect of such a diverse mixture of chemical compounds contained in the plant extracts used in this study. While it is possible that the hypoglycemic effects of the plant extracts may be due, at least in part, to their terpenoid and/or coumarin contents, the mechanism of their hypoglycemic action remains largely speculative. However, this is unlikely to be due to the stimulation of pancreatic beta-cells and subsequent secretion of insulin. Although A. occidentale stem-bark aqueous or methanolic extract is less potent than insulin as an antidiabetic agent, the results of this experimental animal study indicate that it possesses hypoglycemic activity, and thus lends credence to the folkloric use of the plant in the management and/or control of adult-onset, type-2 diabetes mellitus among the Yoruba-speaking people of Western Nigeria.     

The non-ABC drug transporter RLIP76 (RALBP-1) plays a major role in the mechanisms of drug resistance

RLIP76 or Ral binding protein (RalBP-1) was initially cloned as a Ral-effector that was proposed as a link between Ral and Ras pathways. This protein is encoded in humans on chromosome 18p11.3 by a gene with 11 exons and 9 introns and is found ubiquitously from drosophila to humans. RLIP76 displays inhibitory GTPase activity toward Rho/Rac class G-protein cdc42 which is involved in regulation of cytoskeletal organization, lamellipodia, cell migration and apoptosis via Ras. We have recently shown that RLIP76 is also a multispecific transporter of chemotherapeutic agents and glutathione conjugates (GS-E). In human cells RLIP76 accounts for more than two third of the transport activity for GS-E and drugs as opposed to the ABC-transporters including MRP1, which account for less than one third of this activity. Evidence is mounting that RLIP76 is a stress-responsive multi-specific, non-ABC transporter which represents an entirely novel link between stress-inducible G-protein signaling, receptor tyrosine-kinase signaling, endocytosis, heat-shock and stress defense pathways, and transport mediated drug-resistance. The expression of RLIP76 is significantly greater in human cancer cells of diverse origin as compared to the non-malignant cells. Inhibition of RLIP76, using antibodies towards a cell surface epitope, or depletion of RLIP76 using either siRNA or anti-sense phosphorothioate oligonucleotides preferentially causes apoptosis in malignant cells. Administration of RLIP76 antibodies, siRNA, or anti-sense oligonucleotides to mice bearing syngeneic B16 mouse melanoma tumors causes rapid and complete regression of tumors. Studies summarized in this review strongly suggest that RLIP76 is a logical target for clinical intervention of not only multi-drug resistance but also for diseases resulting from oxidative stress.     

Endogenously generated 2-arachidonoylglycerol plays an inhibitory role in bombesin-induced activation of central adrenomedullary outflow in rats

We previously reported the involvement of brain diacylglycerol lipase and cyclooxygenase in intracerebroventricularly (i.c.v.) administered bombesin-induced secretion of noradrenaline and adrenaline from the adrenal medulla in rats. Diacylglycerol can be hydrolyzed by diacylglycerol lipase into 2-arachidonoylglycerol, which may be further hydrolyzed by monoacylglycerol lipase into arachidonic acid, a substrate of cyclooxygenase. 2-Arachidonoylglycerol is a major endocannabinoid, which can inhibit synaptic transmission by presynaptic cannabinoid CB(1) receptors. Released 2-arachidonoylglycerol is rapidly inactivated by uptake into cells and enzymatic hydrolysis. In the present study, we examined the involvement of brain 2-arachidonoylglycerol and its regulatory role in the bombesin-induced central activation of adrenomedullary outflow using anesthetized rats. The elevation of plasma noradrenaline and adrenaline induced by a sub-maximal dose of bombesin (1 nmol/animal, i.c.v.) was reduced by MAFP (monoacylglycerol lipase inhibitor) (0.28 and 0.7 μmol/animal, i.c.v.), JZL184 (selective monoacylglycerol lipase inhibitor) (0.7 and 1.4 μmol/animal, i.c.v.), ACEA (CB(1) receptor agonist) (0.7 and 1.4 μmol/animal, i.c.v.) and AM 404 (endocannabinoid uptake-inhibitor) (80 and 250 nmol/animal, i.c.v.), while AM 251 (CB(1) receptor antagonist) (90 and 180 nmol/animal, i.c.v.) potentiated the response induced by a small dose of bombesin (0.1 nmol/animal, i.c.v.). These results suggest a possibility that 2-arachidonoylglycerol is endogenously generated in the brain during bombesin-induced activation of central adrenomedullary outflow, thereby inhibiting the peptide-induced response by activation of brain CB(1) receptors in rats.     

Lipid-lowering effect of Rhus coriaria L. (sumac) fruit extract in hypercholesterolemic rats

Hyperlipidemia is a major risk factor for development of atherosclerosis. In the present study, the hypolipidemic effects of sumac (Rhus coriaria L.) fruits in high cholesterold diet (HCD)-fed rats was investigated. There was a significant (p < 0.001) increase in the levels of total cholesterol (TC) and triglycerides (TG) along with augmented activities of serum aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase. Treatment with aqueous methanol extract of sumac fruits reduced the above alterations observed in hypercholesterolemic rats. Sumac extract also reversed the hypertrophic cardiac histology. Furthermore, in vivo toxicological studies showed no evidence of acute toxicity of the extract in male Wistar rats. In conclusion, sumac fruit extract intervention minimized the lipid abnormalities and abnormal biochemical changes induced in HCD fed rats. This shows that sumac fruit extract possesses cardioprotective and hepatoprotective activities which will be beneficial in hypercholesterolemic condition.     

Chronic administration of the oral hypoglycaemic agent diphenyleneiodonium to rats. An animal model of impaired oxidative phosphorylation (mitochondrial myopathy)

Daily subcutaneous administration of the oral hypoglycaemic agent, diphenyleneiodonium at a low dose (1.5 mg/kg body weight) over a 4-5 week period resulted in a normoglycaemic stable animal model of impaired oxidative phosphorylation in the rat. Diphenyleneiodonium specifically inhibits NAD-linked mitochondrial oxidation [Bloxham, Biochem. Soc. Trans. 7, 103 (1979)], and in isolated mitochondrial preparations from heart, soleus and gastrocnemius muscle and liver from treated animals NAD-linked respiration was reduced by 40% or more of mean control values. Brain and kidney mitochondria isolated from the treated group had similar rates of NAD-linked respiration to their respective control values. The activity of NADH-ferricyanide reductase was significantly reduced in all tissues tested, even in the isolated brain and kidney mitochondria where the activity in these tissues was 60-75% of control values. This suggests that at least 40% of Complex I activity must be inhibited before there is a decline in NAD-linked mitochondrial respiration. This paper discusses the use of diphenyleneiodonium as a means of establishing an animal model of the human disease state, termed mitochondrial myopathy.     

The bialaphos resistance gene (bar) plays a role in both self-defense and bialaphos biosynthesis in Streptomyces hygroscopicus

We inactivated the bialaphos (BA) resistance gene (bar) of a BA producer, Streptomyces hygroscopicus, by the gene replacement technique. The resulting BA-sensitive mutant (Bar-) was able to produce little BA but considerable amount of an intermediate demethylphosphinothricin (DMPT). The Bar- mutant was still able to convert the N-acetyl derivative (AcDMPT) of DMPT to BA. Introduction of normal bar containing plasmid restored both BA resistance and BA biosynthesis to levels as high as the parental BA producer. By contrast, introducing a multi copy glutamine synthetase gene (glnA) into the Bar- mutant restored BA resistance but not BA production. Thus, the bar gene plays a crucial role in both self-defense and a step of BA biosynthesis in the BA-producing S. hygroscopicus.     

Healing effect of Dillenia indica fruit extracts standardized to betulinic acid on ultraviolet radiation-induced psoriasis-like wounds in rats

Context: Dillenia indica Linn. (Dilleniaceae) is traditionally used to treat skin inflammation.

Objective: This study evaluated the healing effect of Dillenia indica fruit extracts on induced psoriasis-like wounds in Wistar rats.

Materials and methods: Extracts were standardized to betulinic acid, including an aqueous ethanolic extract (AEE), ethyl acetate extract (EAE) and petroleum ether extract. Effects against lipid peroxidation were assessed in vitro. Wounds were created at rat tails (n?=?12). Topical treatments were applied once daily for 7 days (1?mL of AEE or EAE at 5 or 50?mg/mL). Maximal dose was defined by the extract solubility. A 10-fold lower dose was also tested. Positive and negative controls were treated with clobetasol (0.5?mg/mL) or excipient. Half of each group was euthanized for histology. The remaining animals were observed for 20 days for wound measurements.

Results: Yields of AEE and EAE were 4.3 and 0.7%, respectively. Betulinic acid concentrations in AEE and EAE were 4.6 and 107.6?mg/g. Extracts neutralized lipid peroxidation in vitro at 0.02?μg/mL, accelerating healing at 50?mg/mL. Complete healing in mice treated with AEE occurred 16 days after wound induction. This time was 14 and 12 days in mice treated with EAE and clobetasol. Compared to orthokeratosis, parakeratosis was reduced by AEE (25%), EAE (45%) and clobetasol (55%). EAE caused superior protection against biomolecules oxidation of skin compared to AEE.

Discussion and conclusion: EAE exhibited activity closer to that of clobetasol. Betulinic acid may be an active constituent, which should be assessed in future studies.     

Platelet-activating factor (PAF) plays an important role in the immediate asthmatic response in guinea-pig by augmenting the response to histamine.

1. To investigate the role of platelet activating factor (PAF) in the immediate asthmatic response, we examined the bronchial reactivity to histamine after administration of PAF to guinea-pigs or antigen challenge to passively sensitized guinea-pigs. 2. A bolus injection of PAF (20-40 ng kg-1), which did not cause a significant increase in intrathoracic pressure (ITP), augmented the bronchial response to histamine almost 8 fold. This airway hyperreactivity was observed even 1 min after PAF treatment. 3. A subthreshold dose of antigen (0.01 mg kg-1, i.v.) also provoked hyperreactivity to histamine, which became significant 6 and 11 min after the antigen treatment. 4. The specific PAF-antagonists, SM-10661 and CV-6209 (i.v.) dose-dependently inhibited both PAF- and antigen-induced airway hyperreactivities to histamine. 5. These results suggest that PAF plays an important role in antigen-induced acute airway responses by augmenting the activities of spasmogens.