Are anti-inflammatory properties of lipoic acid associated with the formation of hydrogen sulfide?

BACKGROUND: Lipoic acid (LA) was shown to possess anti-inflammatory properties. In this study, we present evidence supporting the hypothesis that the anti-inflammatory properties of LA are associated with the formation of hydrogen sulfide (H2S). METHODS: The study was conducted on male albino Swiss mice. The animals were treated with carrageenan by subcutaneous (sc) injection into the right hind paw to induce acute inflammation. Animals were treated intraperitoneally (ip) with LA (30, 50 and 100 mg/kg) or indomethacin (20 mg/kg) 30 min before carrageenan administration. The control group was given ip the vehicle (1% Tween 80) 30 min before carrageenan administration. Additional experiment involved ip combined treatment of mice with glibenclamide (10 mg/kg) or glibenclamide (10 mg/kg) and LA(100 mg/kg) 30 min before carrageenan administration. LA, indomethacin and glibenclamide were suspended in 1% Tween 80. At 1, 2 and 3 h after treatment with carrageenan the degree of the paw edema was evaluated by the measurement of the paw volume using aqueous plethysmometer. RESULTS: Injection of carrageenan into the mouse hind paw increased paw volume. The increase in paw edema was completely suppressed by pretreatment with LA. The reduction of paw edema by LA was abolished by pretreatment with the K(ATP) channel antagonist, glibenclamide. CONCLUSION: Our findings demonstrate for the first time in vivo that the anti-inflammatory activity of LA might be connected with the formation of H2S.

Combined effect of sesamin and α-lipoic acid on hepatic fatty acid metabolism in rats.

PURPOSE: Dietary sesamin (1:1 mixture of sesamin and episesamin) decreases fatty acid synthesis but increases fatty acid oxidation in rat liver. Dietary α-lipoic acid lowers hepatic fatty acid synthesis. These changes can account for the serum lipid-lowering effect of sesamin and α-lipoic acid. It is expected that the combination of these compounds in the diet potentially ameliorates lipid metabolism more than the individual compounds. We therefore studied the combined effect of sesamin and α-lipoic acid on lipid metabolism in rats. METHODS: Male Sprague-Dawley rats were fed diets supplemented with 0 or 2 g/kg sesamin and containing 0 or 2.5 g/kg α-lipoic acid for 22 days. RESULTS AND CONCLUSIONS: Sesamin and α-lipoic acid decreased serum lipid concentrations and the combination of these compounds further decreased the parameters in an additive fashion. These compounds reduced the hepatic concentration of triacylglycerol, the lignan being less effective in decreasing this value. The combination failed to cause a stronger decrease in hepatic triacylglycerol concentration. The combination of sesamin and α-lipoic acid decreased the activity and mRNA levels of hepatic lipogenic enzymes in an additive fashion. Sesamin strongly increased the parameters of hepatic fatty acid oxidation enzymes. α-Lipoic acid antagonized the stimulating effect of sesamin of fatty acid oxidation through reductions in the activity of some fatty acid oxidation enzymes and carnitine concentration in the liver. This may account for the failure to observe strong reductions in hepatic triacylglycerol concentration in rats given a diet containing both sesamin and α-lipoic acid.

Inflammation and apoptosis in aortic tissues of aged type II diabetes: amelioration with alpha-lipoic acid through phosphatidylinositol 3-kinase/Akt- dependent mechanism.

AIMS: Endothelial dysfunction is a key triggering event in the development of cardiovascular diseases and the current study explored this phenomenon in the context of inflammation, apoptosis, reactive oxygen species (ROS) and the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway during chronic diabetes. MAIN METHODS: alpha-Lipoic acid (ALA) and wortmannin (WM) were chronically administered to aged Goto Kakizaki (GK) rats, a genetic model of non-obese type II diabetes. Key indices of inflammation, apoptosis and oxidative stress were assessed using western blotting, real-time PCR and immunofluoresence-based techniques. KEY FINDINGS: A chronic inflammation (e.g., increased mRNA/protein levels of TNF-alpha, ICAM, fractalkine, CD-68, myeloperoxidase) in connection with increased caspase-based apoptotic cell death and heightened state of oxidative stress (HSOS)- appear to exist in diabetic cardiovascular tissues. An assessment of NF-kappaB dynamics in aged diabetic vessels revealed not only a marked increase in cytosolic phosphorylated levels of IkappaB-alpha, NIK, IKK but also an enhancement in nuclear localization of p65 concomitantly with augmented NF-kappaB-DNA binding activity. Most of the aforementioned cardiovascular-based diabetic abnormalities including reduced activities of PI3K and Akt kinase were ameliorated following chronic ALA therapy. WM, given to GK rats negated the anti-inflammatory and anti-apoptotic actions of ALA. SIGNIFICANCE: Our data highlight a unifying mechanism whereby HSOS through an induction of NF-kappaB activity together with an impairment in PI3K/Akt pathway favors pro-inflammatory/pro-apoptotic diabetic vascular milieu that culminate in the onset of endothelial dysfunction, a phenomenon which appears to be amenable to treatment with antioxidants and/or PI3/Akt mimetics (e.g., ALA).

Lipoic acid prevents suppression of connective tissue proliferation in the rat liver induced by n-3 PUFAs. A pilot study.

As previously shown, dietary n-3 polyunsaturated fatty acids (n-3 PUFAs) suppress connective tissue proliferation in the rat liver wound concurrent with an elevated level of lipid peroxidation. The present study was undertaken to investigate the influence of alpha-lipoic acid (LA), a natural anti-oxidant, on these effects of n-3 PUFAs. Rats were fed with a commercial pellet diet (control group) or with diets enriched with 10% of sunflower oil (n-6 group) or 10% of fish oil (n-3 group) for 8 weeks followed by addition of LA to the same diets for 10 days. Then a liver thermic wound was induced and the administration of LA was continued for 6 days. The proliferation of the connective tissue, the level of lipid peroxidation and their peroxidizability and the content of prostaglandins E2 and F2alpha were measured in the liver wounds. LA prevented the suppression of connective tissue proliferation in the healing wound induced by n-3 PUFAs, avoided the increase in peroxidation of lipids, reduced peroxidizability of lipids and modulated the decrease in PGE2 and PGF2alpha. The results indicate that dietary LA may prevent the suppression of liver wound healing induced by n-3 PUFAs.

Hepatic lipoate uptake.

Uptake of [35S]lipoate was studied in perfused rat liver and in isolated rat hepatocytes. During single-pass perfusion of [35S]lipoate about 30% of the radioactivity is retained in the liver. A substantial amount of 5,5'-dithiobis(2-nitrobenzoic acid)-reactive material appears in the effluent perfusate, while hepatic efflux of GSH is unchanged. The hepatic uptake of lipoate, the release of thiols, and also the biliary excretion of 35S-labeled compounds are suppressed by octanoate. In isolated hepatocytes the uptake of lipoate follows saturation kinetics showing a Km value of 38 microM and a Vmax of 180 pmol/mg X 10 s. The uptake is temperature-dependent; from the Arrhenius plot an activation energy of 14.8 kcal/mol at 20 microM lipoate is calculated. At high concentrations of lipoate (above 75 microM) a nonsaturable uptake component becomes predominant. Lipoate uptake is selectively inhibited by medium-chain fatty acids. Only slight inhibition is seen in the presence of long-chain fatty acids, and there is no inhibition with acetate or lactate. Substantial inhibition is also observed with acetylsalicylic acid, but not with taurocholate, bromosulfophthalein or biotin. Lipoate uptake can be inhibited by high concentrations of phloretin (200 microM) and is rather insensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (200 microM). The results indicate that hepatic uptake of lipoate at physiological concentrations is largely carrier-mediated.

Role of oxalacetate in lipoate effect on frog gastric mucosa.

The mechanism of action of lipoate on frog gastric mucosa was investigated. Oxalacetate (OAA) reversed lipoate-inhibited QO2 and QH+ of chambered mucosas by 70 and 40%, respectively. Pyruvate or glucose produced similar effects. Neither activity was affected by OAA when added after glucose, pyruvate, decanoate, butyrate, or lipoate-propionate-inhibited mucosa. Lipoate-treated or lipoate-propionate-treated mucosa did not respond to histamine; OAA addition prior to histamine restored responsiveness. Tracer and chromatographic techniques showed that lipoate reduced and pyruvate increased OAA formation. Preincubation of mitochondrial extracts of gastric mucosa with 2 mM lipoate increased pyruvic dehydrogenase activity 110%. Pyruvic carboxylase (PC) activity was primarily in the mitochondrial fraction of the gastric mucosa. The PC preparation was shown to have an absolute requirement for CoASAc, contained biotin, was not inhibited by lipoate, and had an apparent Km approximately equal to 3.6 X 10(-4) M for pyruvate. The results suggest that OAA concentration is regulated by PC activity and is one of the factors controlling QO2 and QH+ in the frog gastric mucosa.

Selective inactivation of the transacylase components of the 2-oxo acid dehydrogenase multienzyme complexes of Escherichia coli.

1. The reaction of the pyruvate dehydrogenase multienzyme complex of Escherichia coli with maleimides was examined. In the absence of substrates, the complex showed little or no reaction with N-ethylmaleimide. However, in the presence of pyruvate and N-ethylmaleimide, inhibition of the pyruvate dehydrogenase complex was rapid. Modification of the enzyme was restricted to the transacetylase component and the inactivation was proportional to the extent of modification. The lipoamide dehydrogenase activity of the complex was unaffected by the treatment. The simplest explanation is that the lipoyl groups on the transacetylase are reductively acetylated by following the initial stages of the normal catalytic cycle, but are thereby made susceptible to modification. Attempts to characterize the reaction product strongly support this conclusion. 2. Similarly, in the presence of N-ethylmaleimide and NADH, much of the pyruvate dehydrogenase activity was lost within seconds, whereas the lipoamide dehydrogenase activity of the complex disappeared more slowly: the initial site of the reaction with the complex was found to be in the lipoyl transacetylase component. The simplest interpretation of these experiments is that NADH reduces the covalently bound lipoyl groups on the transacetylase by means of the associated lipoamide dehydrogenase component, thereby rendering them susceptible to modification. However, the dependence of the rate and extent of inactivation on NADH concentration was complex and it proved impossible to inhibit the pyruvate dehydrogenase activity completely without unacceptable modification of the other component enzymes. 3. The catalytic reduction of 5,5'-dithiobis-(2-nitrobenzoic acid) by NADH in the presence of the pyruvate dehydrogenase complex was demonstrated. A new mechanism for this reaction is proposed in which NADH causes reduction of the enzyme-bound lipoic acid by means of the associated lipoamide dehydrogenase component and the dihydrolipoamide is then oxidized back to the disulphide form by reaction with 5,5'-dithiobis-(2-nitrobenzoic acid). 4. A maleimide with a relatively bulky N-substituent, N-(4-diemthylamino-3,5-dinitrophenyl)maleimide, was an effective replacement for N-ethylmaleimide in these reactions with the pyruvate dehydrogenase complex. 5. The 2-oxoglutarate dehydrogenase complex of E. coli behaved very similarly to the pyruvate dehydrogenase complex, in accord with the generally accepted mechanisms of the two enzymes. 6. The treatment of the 2-oxo acid dehydrogenase complexes with maleimides in the presence of the appropriate 2-oxo acid substrate provides a simple method for selectively inhibiting the transacylase components and for introducing reporter groups on to the lipoyl groups covalently bound to those components.