Ameliorating effect of selenium on chromium (VI)-induced oxidative damage in the brain of adult rats

Chromium is known for its wide toxic manifestations. This experiment aims to evaluate the effect of selenium against oxidative stress induced by chromium in the cerebrum and cerebellum. Female Wistar rats were randomly divided into four groups of six each: group I served as controls which received the standard diet; group II received drinking water K(2)Cr(2)O(7) alone (700 ppm); group III received both K(2)Cr(2)O(7) and Se (0.5 mg Na(2)SeO(3)/kg of diet); and group IV received Se (0.5 mg/kg of diet) for 3 weeks. The exposure of rats to K(2)Cr(2)O(7) promoted oxidative stress in the cerebrum and cerebellum with an increase in malondialdehyde and a decrease of nonenzymatic antioxidant levels such as glutathione, nonprotein thiol, and vitamin C. An increase of enzyme activities like catalase, glutathione peroxidase, and superoxide dismutase activities was also observed. Acetylcholinesterase activity was inhibited after treatment with K(2)Cr(2)O(7). Co-administration of Se restored the parameters cited above. The histopathological findings confirmed the biochemical results.     

In vivo nephrotoxicity induced in mice by chromium(VI)

The role of glutathione (GSH) and chromium (V) in chromium (VI)-induced nephrotoxicity in mice was investigated at 24 h after K2Cr(VI)2O7 ip injection. Nephrotoxicity was assessed by measurements of relative kidney weight and serum urea nitrogen. Cr(VI) nephrotoxicity was accompanied by decreased renal GSH and glutathione reductase (GSSG-R) levels. Pretreatment with buthionine sulfoximine, an inhibitor of GSH biosynthesis, enhanced Cr(VI)-induced nephrotoxicity, and remarkably diminished kidney GSH and GSSG-R levels. In contrast, pretreatment with glutathione methyl ester, a GSH-supplying agent, prevented Cr(VI) from exerting a harmful effect on mouse kidney and restored kidney GSH level. Administration of a Cr(V) compound, K3Cr(V)O8, induced much higher toxicity in mouse kidney than Cr(VI), but it failed to diminish renal GSH level. Another Cr(V) compound, Cr(V)-GSH complex, and Cr(III) nitrate did not cause a nephrotoxic effect in mice. The mechanism of Cr(VI)-induced nephrotoxicity was explained using GSH and Cr(V).     

Oxidative stress-related lung dysfunction by chromium(VI): alleviation by Citrus aurantium L.

Chromium(VI), a very strong oxidant, causes high cytotoxicity through oxidative stress in tissue systems. Our study investigated the potential ability of ethanolic Citrus aurantium L., family Rutaceae extract, used as a nutritional supplement, to alleviate lung oxidative damage induced by Cr(VI). A high-performance liquid chromatography coupled with a mass spectrometer method was developed to separate and identify flavonoids in C. aurantium L. Six flavonoids were identified, as (1) poncirin, (2) naringin, (3) naringenin, (4) quercetin, (5) isosinensetin, and (6) tetramethyl-o-isoscutellarein. Adult Wistar rats, used in this study, were divided into six groups of six animals each: group I served as controls which received standard diet, group II received via drinking water K₂Cr₂O₇ alone (700 ppm), groups III and IV were pretreated for 10 days with ethanol extract of C. aurantium L. at doses of 100 and 300 mg/kg body weight/day, respectively, and then K₂Cr₂O₇ was administrated during 3 weeks, and groups V and VI received during 10 days only C. aurantium L. ethanol extract at doses of 100 and 300 mg/kg/day, respectively. Ethanol extract of C. aurantium L. was administered orally. Rats exposed to Cr(VI) showed in lung an increase in malondialdehyde and protein carbonyl levels and a decrease in sulflydryl content, glutathione, nonprotein thiol, and vitamins C and E levels. Decreases in enzyme activities such as in Na⁺K⁺ ATPase, catalase, glutathione peroxidase, and superoxide dismutase were noted. Pretreatment with C. aurantium L. of chromium-treated rats ameliorated all biochemical parameters. Lung histological studies confirmed the biochemical parameters and the beneficial role of C. aurantium L.     

Moderate selenium dosing inhibited chromium (VI) toxicity in chicken liver

This study aimed to clarify the effect of selenium (Se) on chromium (VI) [Cr(VI)]‐induced damage in chicken liver. A total of 105 chickens were randomly divided into seven groups of 15. Group I received deionized water; group II received Cr(VI) (7.83 mg/kg/d) alone; and other groups orally received both Cr(VI) (7.83 mg/kg/d) and Se of different doses (0.14, 0.29, 0.57, 1.14, and 2.28 mg/kg/d). The levels of superoxide dismutase (SOD), glutathione (GSH), malondialdehyde (MDA), Ca²⁺‐ATPase, and mitochondrial membrane potential (MMP) were measured. Results showed that Cr(VI) increased MDA content and decreased GSH content, T‐SOD activity, Ca²⁺‐ATPase activity, and MMP level. Meanwhile, Se co‐treatment (0.14, 0.29, and 0.57 mg/kg/d) increased the viability of the above indicators compared with Cr(VI)‐treatment alone. In addition, histopathologic examination revealed that Cr(VI) can cause liver damage, whereas Se supplementation of moderate dose inhibited this damage. This study confirmed that Se exerted protective effect against Cr(VI)‐induced liver damage.     

Myocardial protective effect of octylguanidine against the damage induced by ischemia reperfusion in rat heart

This study shows that the hydrophobic cation octylguanidine protects against myocardial damage induced by ischemia-reperfusion. The protective effect of the amine was analyzed after 5 min of coronary occlusion followed by 5 min reperfusion in rat hearts. ECG tracings from rats treated with an i.v. injection of 5 mg/kg of octylguanidine showed a total absence of post-reperfusion arrhythmias, conversely to what was observed in untreated rats. The histological images showed that myocardium fibers from treated rats were in good shape and retained their striae, also there was absence of edema. Furthermore, the accumulation of ²⁰¹Tl in hearts from these rats indicated that the tissue did not suffer disruption or impairment in membrane functions. The above correlated with the fact that mitochondria isolated from the ventricular free wall from treated rats preserved their ability to synthesize ATP. We propose that the protective effect of octylguanidine might be due to its documented inhibitory action on the opening of mitochondrial non-specific pores, a mechanism which is associated in heart injury as induced by reperfusion. (Mol Cell Biochem 269: 19–26, 2005)     

Binding of chromium(VI) to histones: implications for chromium(VI)-induced genotoxicity

The first evidence has been obtained for Cr(VI) (chromate) binding to isolated calf thymus (CT) histones under physiological conditions (pH 7.4, Cl⁻ concentration 152 mM, 310 K). No significant Cr(VI) binding under the same conditions was observed for other extracellular and intracellular proteins, including albumin, apo-transferrin and G-actin, as well as for CT DNA. The mode of Cr(VI) binding to histones was studied by vibrational, electronic and X-ray absorption (X-ray absorption near-edge structure and X-ray absorption fine structure) spectroscopies and molecular mechanics calculations. A proposed binding mechanism includes electrostatic interactions of CrO₄ ²⁻ with protonated Lys and Arg residues of histones, as well as the formation of hydrogen bonds with the protein backbone. Similarly, Cr(VI) can bind to nuclear localization signals (typically, Lys- and Arg-rich fragments) of other nuclear proteins. Selective binding of Cr(VI) to newly synthesized nuclear proteins (including histones) in the cytoplasm is likely to be responsible for the active transport of Cr(VI) into the nuclei of living cells. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Oxidative damage of DNA by chromium(V) complexes: relative importance of base versus sugar oxidation

Chromium(V)-mediated oxidative damage of deoxy-ribonucleic acids was investigated at neutral pH in aqueous solution by utilizing bis(2-ethyl-2-hydroxy-butanato)oxochromate(V) (I) and bis(hydroxyethyl)-amino-tris(hydroxymethyl)methane)oxochromate(V) (II). Single-stranded and double-stranded (ds) calf thymus and human placenta DNA, as well as two oligomers, 5'-GATCTAGTAGGAGGACAAATAGTGTTTG-3' and 5'-GATCCAAGCAAACACTATTTGTCCTCCTACTA-3', were reacted with the chromium(V) complexes. Most products were separated and characterized by chroma-tographic and spectroscopic methods. Polyacrylamide gel electrophoresis experiments reveal more damage at G sites in comparison to other bases. Three primary oxidation products, 5-methylene-2-furanone (5-MF), furfural and 8-oxo-2'-deoxyguanosine, were characterized. A minor product, which appears to be thymine propenal, was also observed. The dsDNA produces more furfural than furanone. The formation of these two products resulted from hydrogen ion or hydride transfer from C1' and C5' positions of the ribose to the oxo-chromium(V) center. Since no enhancements of these products (except propenal) were observed in the presence of oxygen, mechanisms pertaining to the participation of activated oxygen species may be ruled out. The oxidation of the G base is most likely associated with an oxygen atom transfer from the oxo-metallates to the double bond between C8 and N7 of the purine ring. The formation of the propenal may be associated with an oxygen-activated species, since a marginal enhancement of this product was observed in the presence of oxygen. The formation of furfural in higher abundance over 5-MF for dsDNA was attributed to the ease of hydrogen ion (or hydride transfer) from the C5' compared to C1' position of the ribose within a Cr(V)-DNA intermediate in which the metal center is bound to the phosphate diester moiety.     

Antioxidant-mediated protective effect of potato peel extract in erythrocytes against oxidative damage

Potato peels are waste by-product of the potato processing industry. They are reportedly rich in polyphenols. Our earlier studies have shown that extracts derived from potato peel (PPE) possess strong antioxidant activity in chemical and biological model systems in vitro, attributable to its polyphenolic content. The main objective of this study was to investigate the ability of PPE to protect erythrocytes against oxidative damage, in vitro. The protection rendered by PPE in erythrocytes was studied in terms of resistance to oxidative damage, morphological alterations as well as membrane structural alterations. The total polyphenolic content in PPE was found to be 3.93 mg/g powder. The major phenolic acids present in PPE were predominantly: gallic acid, caffeic acid, chlorogenic acid and protocatechuic acid. We chose the experimental prooxidant system: FeSO₄ and ascorbic acid to induce lipid peroxidation in rat RBCs and human RBC membranes. PPE was found to inhibit lipid peroxidation with similar effectiveness in both the systems (about 80–85% inhibition by PPE at 2.5 mg/ml). While PPE per se did not cause any morphological alteration in the erythrocytes, under the experimental conditions, PPE significantly inhibited the H₂O₂-induced morphological alterations in rat RBCs as revealed by scanning electron microscopy. Further, PPE was found to offer significant protection to human erythrocyte membrane proteins from oxidative damage induced by ferrous–ascorbate. In conclusion, our results indicate that PPE is capable of protecting erythrocytes against oxidative damage probably by acting as a strong antioxidant.     

Effects of chromium(VI) and chromium(III) on energy charge and oxygen consumption in rat thymocytes

The cytotoxic effects of chromium compounds in two oxidation states have been studied in rat thymocytes. endogenous nucleotide levels and oxygen consumption were examined as relevant parameters of the physiological state of the cell. Incubation of rat thymocytes with Cr(VI) produced a marked unbalance of endogenous purine nucleotide pool and a parallel decrease in oxygen consumption. A close correlation between the reduction of oxygen consumption and ATP level in rat thymocytes treated with increasing concentrations of Cr(VI) has been found. In rat thymocytes permeabilized with digitonin and in isolated rat liver mitochondria both Cr(VI) and Cr(III) showed, at different range of concentrations, a marked inhibition of maximal oxygen consumption rate (uncoupled respiration). The effects observed were depending on chromium oxidation state and on different mitochondrial sites of substrate oxidation.     

Mechanisms of DNA damage and insight into mutations by chromium(VI) in the presence of glutathione

The mechanisms of hexavalent chromium(VI) induced DNA damage were unveiled by detecting products of single- and double-stranded DNA in the presence of glutathione. The absence of a detectable hydroxyl radical in the reactions indicates that DNA damage was exclusively by hypervalent chromium species. Polyacrylamide gel electrophoresis (PAGE) experiments with 32-mer single-stranded oligonucleotide and its complementary duplex revealed cleavages largely at purine bases with significant enhancement of such cleavages in the presence of a base. Quantitative estimations of bases released by HPLC before and after enzymatic digestion with exonucleases unequivocally established the excessive release of purine bases. This release was accompanied by the concomitant formation of phosphoglycolate as characterized by liquid chromatography-mass spectrometry (LC-MS). These data connote that the preponderance DNA damage is due to an oxidation specifically at H4' of the ribose moiety leading to the formation of apurinic sites. In addition to the oxidation at H4', DNA oxidation was also initiated through H5' site as evidenced by the identification of furfural. This pathway appears to be non-selective and more abundant for ssDNA as cleavages were observed at both purine and pyrimidine bases. Finally, the detection of guanidinohydantoin as a minor product points the involvement of an oxygen activated hypervalent chromium species, perhaps a peroxo-chromium species. Both major and minor pathways lead to cleavages at purine sites for ds-DNA and are consistent with the observation that DNA cleavage was enhanced in the presence of a base. In contrast, when hydrogen peroxide was added to the reactions, random DNA cleavages were apparent indicating involvement of multiple species including a hydroxyl radical. These data pinpoint mutation mechanisms induced by chromium(VI) in the presence of glutathione due to transversion either by inserting the wrong bases opposite to the apurinic sites during replication or by purine-purine mismatch.     

Ameliorative action of melatonin on oxidative damage induced by atrazine toxicity in rat erythrocytes

Excessive generation of reactive oxygen species (ROS) can induce oxidative damage to vital cellular molecules and structures including DNA, lipids, proteins, and membranes. Recently, melatonin has attracted attention because of their free radical scavenging and antioxidant properties. The aim of this study was to evaluate the possible protective role of melatonin against atrazine-induced oxidative stress in rat erythrocytes in vivo. Adult male albino rats of Wistar strain were randomly divided into four groups. Control group received isotonic saline; melatonin (10 mg/kg bw/day) group; atrazine (300 mg/kg of bw/day) group; atrazine + melatonin group. Oral administration of atrazine and melatonin was given daily for 21 days. Oxidative stress was assessed by determining the glutathione (GSH) and malondialdehyde (MDA) level, and alteration in antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), glutathione-S-transferase (GST), and glucose-6-phosphate dehydrogenase (G-6-PD) in the erythrocytes of normal and experimental animals. A significant increase in the MDA levels and decrease in the GSH was observed in the atrazine treated animals (P < 0.05). Also, significant increase in the activities of SOD, CAT, GPx, and GST were observed in atrazine treated group compared to controls (P < 0.05). Moreover, significant decrease in protein, total lipids, cholesterol, and phospholipid content in erythrocyte membrane were demonstrated in atrazine treated rats. Administration of atrazine significantly inhibits the activities of G-6-PD and membrane ATPases such as Na(+)/K(+)-ATPase, Mg(2+)-ATPase, and Ca(2+)-ATPase (P < 0.05). Scanning electron microscopic (SEM) examination of erythrocytes revealed morphological alterations in the erythrocytes of atrazine treated rats. Furthermore, supplementation of melatonin significantly modulates the atrazine-induced changes in LPO level, total lipids, total ATPases, GSH, and antioxidant enzymes in erythrocytes. In conclusion, the increase in oxidative stress markers and the concomitant alterations in antioxidant defense system indicate the role of oxidative stress in erythrocytes of atrazine-induced damage. Moreover, melatonin shows a protective role against atrazine-induced oxidative damage in rat erythrocytes.     

Mechanism of chromium(VI) carcinogenesis

Since chromium(VI) is unreactive toward DNA under physiological conditions in vitro, the ability of carcinogenic chromium(VI) compounds to damage DNA depends on the presence of cellular redox components that reduce chromium(VI) to reactive species capable of interacting with DNA. We have examined the role of glutathione and hydrogen peroxide in chromium(VI)-induced DNA damage in vitro. Upon reaction with chromium(VI), glutathione produced chromium(V) and glutathione thiyl radical reactive intermediates, whereas hydrogen peroxide produced chromium(V) and hydroxyl radical. Reaction of DNA with chromium(VI) in the presence of glutathione resulted in binding of chromium and glutathione to DNA with little or no DNA strand breakage. Reaction of DNA with chromium(VI) in the presence of hydrogen peroxide produced the 8-hydroxydeoxy-guanosine adduct and extensive DNA strand breakage in the absence of significant Cr-DNA adduct formation. These results suggest that the nature of chromium(VI)-induced DNA damage will be strongly dependent on reactive intermediates such as chromium(V), glutathione thiyl radical, and hydroxyl radical, produced by cellular components active in chromium(VI) metabolism. In order to assess the ability of chromium(VI)-induced DNA damage to affect the normal template function of DNA, we investigated the effects of chromium(VI) on steady-state mRNA levels of various genes in chick embryo liver in vivo, and compared the effects to the levels of DNA damage observed. Chromium(VI) induced DNA-protein and DNA interstrand cross-links in chick embryo liver in vivo and suppressed the induction of 5-aminolevulinic acid synthase and cytochrome P-450 mRNA expression by porphyrinogenic drugs. In contrast, chromium(VI) increased the basal levels of expression of these two inducible genes, but had little or no effect on the expression of the constitutive albumin, β-actin, and conalbumin genes. Comparison of the time course of formation and repair of DNA damage with that of changes in gene expression suggests that chromium(VI) may form a mono-adduct prior to formation of DNA cross-links, and that chromium(VI)-induced DNA lesions may target certain classes of genes and lead to changes in their expression.     

Reduction of chromium (VI) by reference bacterial strains

Collection bacterial strains were found to be capable of chromium (VI) reduction although they had not been in contact with chromium compounds before. Strains capable of nitrate respiration could use bichromate ions as a terminal electron acceptor in the absence of competing acceptors. Cr(VI) was reduced to Cr(III) when bichromate was added to the cultural broth whose redox potential reached -140 mV.     

UVB-induced hemolysis of rat erythrocytes: protective effect of procyanidins from grape seeds

Besides erythema and sunburn reactions, UVB stress can promote erythrocyte extravasation from skin capillaries and hemolysis, and photosensitized hemoglobin can in turn lead to an overload of free radicals in dermis which exacerbates photodamage. The objective of this study was to investigate in rat erythrocytes (RBC) the pattern of events leading to membrane peroxidation and hemolysis following UVB insult (1.5-8.5 J/cm2), and the protective action of grape seed procyanidins. UVB causes a dramatic dose-dependent decrease of intracellular glutathione (paralleled by the formation of pro-oxidant ferryl-hemoglobin), of intramembrane vitamin E and of membrane fluidity, then a rise of conjugated dienes (CD), and thiobarbituric acid-reactive substances (TBARS) and finally a strong hemolytic effect. Procyanidins prevent membrane peroxidation (but not intracellular GSH depletion nor ferryl-hemoglobin formation), with a minimal effective concentration of 0.1 microM (IC50 for TBARS and CD after 120 min UVB exposure: 0.71 microM and 0.56 microM) and dose-dependently delay the onset of hemolysis, by 30 min at 0.1 mciroM, by 90 and 120 min at 0.5 and 1.0 microM. Epigallocatechin-3-O-gallate (EGCG) and catechin, typical constituents of the fraction, were significantly less potent. This since procyanidins (1 microM) inhibit the formation of phospholipid hydroperoxides of the inner (phosphatidylserine, phosphatidylethanolamine) and outer (phosphatidylcholine) layers of the RBC membrane (HPLC analysis), suppress the decrease in membrane fluidity due to lipid and protein thiol oxidation and spare vitamin E from consumption in a dose-dependent manner (0.1-1 microM). Hence procyanidins, preserving membrane phospholipids, since their strong antilipoperoxidant activity, may maintain in vivo the integrity of RBC in sub-epidermal capillaries and effectively counteract in dermis the onset/exacerbation of the UVB-induced skin photodamage.     

Effect of selenium compounds on the damage induced by oxysterol on rat arterial walls

Wistar rats were fed Se-deficient (0.017±0.002 mg Se/kg) and Seadequate (0.32±0.045 Se mg/kg) diets for 12 mo and then were given 5 mg/kg of cholestane-3β,tα,6β-triol (3-triol), intravenously. Se compounds (Na₂SeO₃ and ebselen) were supplemented in different doses and times to the Se-deficient rats. Twenty-four hours after 3-triol infusion, the changes in ultrastructures of rat aorta were examined by scanning electron micrography (SEM) and transmission electron micrography (TEM). SEM examinations showed that 3-triol induced diffused injuries on arterial endothelial urfaces of long-term Se-deficient rat, and a large number of holes or craterlike defects were observed. TEM examinations further showed that 3-triol induced swelling, necrosis, and shedding of endothelial cells, which resulted in the destruction of endothelial integrity. Mean-while, smooth muscle cells proliferated and migrated toward intimae; the breakage of internal elastic lamina benefited the migration of smooth muscle cells. Supplemented with Na₂SeO₃ (40 μg/kg, 10 d per continuum) and ebselen (20 mg/kg), respectively, exhibited significant protection from damages induced by 3-triol. It seems that protecting mechanisms were different between Na₂SeO₃ and ebselen. The present investigation gave visual evidence that both injuries induced by cholesterol oxides and the Se nutritional status contributed to the development of atherosclerosis.     

Reduction of chromium(VI) by D-galacturonic acid and formation of stable chromium(V) intermediates

The interaction of dichromate with D-galacturonic acid in aqueous solution, as a function of pH, is described. The reaction involves the reduction of Cr(VI) to Cr(III), but the reaction rate is remarkably dependent on pH. In fact, the reduction of Cr(VI) to Cr(III) proceeds rather quickly in strongly acidic solutions, while it is slow in neutral or moderately acidic media. In all cases, according to the ESR evidence, Cr(V) species are found as intermediates. The stability of the Cr(V) species increases with increasing pH, so that it may be suggested that the overall reaction rate is controlled by the Cr(V) to Cr(III) conversion.     

Acephate induced oxidative damage in erythrocytes

The effect of oral administration of acephate (360 mg/kg body weight), for 15 days, daily, was investigated on the erythrocytes of male rats. Activities of acetyl cholinesterase and glucose-6-phosphate dehydrogenase decreased, while those of glutathione-s-transferase and glutathione reductase increased. Decreased glutathione content and increased lipid peroxidation suggest that there was increased oxidative stress in the erythrocytes of treated animals. Increased cholesterol/phospholipid ratio in the erythrocyte membranes and morphological changes in RBCs (scanning electron microscopy studies) were observed in acephate treated animals. The results clearly suggest that acephate induced oxidative stress in erythrocytes leads to morphological changes.     

Biosorption of aqueous chromium(VI) by Tamarindus indica seeds

The effectiveness of low cost agro-based materials namely, Tamarindus indica seed (TS), crushed coconut shell (CS), almond shell (AS), ground nut shell (GS) and walnut shell (WS) were evaluated for Cr(VI) removal. Batch test indicated that hexavalent chromium sorption capacity (q(e)) followed the sequence q(e)(TS) > q(e)(WS) > q(e)(AS) > q(e)(GS) > q(e)(CS). Due to high sorptive capacity, tamarind seed was selected for detailed sorption studies. Sorption kinetic data followed first order reversible kinetic fit model for all the sorbents. The equilibrium conditions were achieved within 150 min under the mixing conditions employed. Sorption equilibria exhibited better fit to Freundlich isotherms (R>0.92) than Langmuir isotherm (R approximately = 0.87). Hexavalent chromium sorption by TS decreased with increase in pH, and slightly reduced with increase in ionic strength. Cr(VI) removal by TS seems to be mainly by chemisorption. Desorption of Cr(VI) from Cr(VI) laden TS was quite less by distilled water and HCl. Whereas with NaOH, maximum desorption achieved was about 15.3%. When TS was used in downflow column mode, Cr(VI) removal was quite good but head loss increased as the run progressed and was stopped after 200 h.     

Immunomodulatory effects of seabuckthorn (Hippophae rhamnoides L.) against chromium (VI) induced immunosuppression

The present study reports the immunomodulatory effects of seabuckthorn (Hippophae rhamnoides L.) leaf extract on cellular and humoral immune response by studying delayed-type hypersensitivity response, IL-2, IL-4 and γ-IFN levels and antibody titres in chromium-induced immunosuppressed animals. Oral feeding of chromium (30 mg/kg bw) significantly inhibited antibody production and S-RBC induced delayed-type hypersensitivity response. Administration of leaf extract (100 mg/kg bw) along with chromium significantly inhibited chromium-induced immunosuppression. To understand the immunomodulatory mechanism of leaf extract, in vitro studies were carried out using rat lymphocytes. Addition of chromium resulted in a significant decrease in lymphocyte size and increased ROS generation. The leaf extract of seabuckthorn significantly inhibited chromium-induced reactive oxygen species (ROS) generation and maintained the cell size identical to that of control cells. Chromium treatment markedly inhibited the mitochondrial transmembrane potential by larger lymphocytes in particular, while the leaf extract restored the same significantly. Chromium also inhibited significantly concanavalin A (ConA) induced IL-2, IL-4 and γ-IFN production in rat lymphocytes. The leaf extract (100 μg/ml) alone stimulated IL-2 and γ-IFN production even in the absence of ConA and also inhibited chromium-induced decline in IL-2 and γ-IFN production but it did not change IL-4 production. These observations suggest that the leaf extract of seabuckthorn has significant immunomodulatory activity and specifically activates the cell-mediated immune response. (Mol Cell Biochem 278: 101–109, 2005)