Lipid peroxidation and sphingolipid alterations in the cerebral cortex and hypothalamus of rats fed a high-protein diet.

OBJECTIVES: High-protein diets (HPDs) are widely accepted to enhance satiety and energy expenditure and thus have become a popular strategy to lose weight and facilitate muscle protein synthesis. However, long-term high-protein consumption could be linked with metabolic and clinical problems such as renal and liver dysfunctions. This study verified the effects of 8-wk high-protein ingestion on lipid peroxidation and sphingolipid metabolism in the plasma, cerebral cortex, and hypothalamus in rats. METHODS: Immunoenzymatic and spectrophotometric methods were applied to assess oxidation-reduction (redox) biomarkers and neutral sphingomyelinase activity, whereas gas-liquid chromatography and high-performance liquid chromatography were used to examine sphingolipid levels. RESULTS: The vast majority of HPD-related alterations was restricted to the hypothalamus. Specifically, an increased rate of lipid peroxidation (increased lipid hydroperoxides, 8-isoprostanes, and thiobarbituric acid reactive substances) associated with ceramide accumulation via the activation of de novo synthesis (decreased sphinganine), salvage pathway (decreased sphingosine), and sphingomyelin hydrolysis (decreased sphingomyelin and increased neutral sphingomyelinase activity) was noted. CONCLUSIONS: This study showed that HPD substantially affected hypothalamic metabolic pathways, which potentially alter cerebral output signals to the peripheral tissues.

α-Lipoic Acid Supplementation Salivary Glands in the Hyperglycaemic Rats.

BACKGROUND/AIMS: The aim of the present study was to investigate whether α-lipoic acid (ALA) could reverse/prevent high fat diet (HFD) -induced salivary gland dysfunction and oxidative damage in the salivary glands of rats, and strengthen their antioxidant defense. METHODS: The enzymatic and non-enzymatic antioxidants as well as their redox status, oxidative damage products and salivary flow rate were investigated in the parotid (PG) and submandibular (SMG) glands of Wistar rats exposed to a high-fat diet and then supplemented with ALA for a period of 4 weeks. The rats in the study were divided into 4 groups of 10 animals each: C (control), HFD,C + ALA, HFD + ALA. RESULTS: The HFD + ALA group in comparison to the HFD group showed normalization of the activity of antioxidant enzymes to the levels observed in the C group only in the case of the SMG. Additionally, ALA supplementation was more effective in reducing the value of oxidative damage products in the PG compared to the SMG. ALA supplementation in the HFD group was not able to restore the disturbed total antioxidant capacity (TAC) of the salivary glands to the level observed in the C group. In the group of HFD + ALA rats, both unstimulated and stimulated salivation and the protein concentration in the SMG did not differ significantly from the parameters recorded in the group fed with HFD. CONCLUSION: ALA supplementation by rats fed the HFD diet prevents/reverses oxidative damage in the PG to a greater extent than in the SMG and is unable to completely restore disturbed TAC to the levels seen in C rats. Moreover, we observed that ALA supplementation did not improve the impaired secretory function of the salivary glands.

Diverse impact of N-acetylcysteine or alpha-lipoic acid supplementation during high-fat diet regime on fatty acid transporters in visceral and subcutaneous adipose tissue.

PURPOSE: Adipose tissue's (AT) structural changes accompanying obesity may alter lipid transport protein expression and, thus, the fatty acids (FAs) transport and lipid balance of the body. Metabolic abnormalities within AT contribute to the elevated production of reactive oxygen species and increased oxidative/nitrosative stress. Although compounds such as N-acetylcysteine (NAC) and α-lipoic acid (ALA), which restore redox homeostasis, may improve lipid metabolism in AT, the mechanism of action of these antioxidants on lipid metabolism in AT is still unknown. This study aimed to examine the impact of NAC and ALA on the level and FA composition of the lipid fractions, and the expression of FA transporters in the visceral and subcutaneous AT of high-fat diet-fed rats. MATERIALS AND METHODS: Male Wistar rats were randomly divided into four groups. The mRNA levels and protein expression of FA transporters were assessed using real-time PCR and Western Blot analyses. The collected samples were subjected to histological evaluation. The level of lipids (FFA, DAG, and TAG) was measured using gas-liquid chromatography. RESULTS: We found that antioxidants affect FA transporter expressions at both the transcript and protein levels, and, therefore, they promote changes in AT's lipid pools. One of the most remarkable findings of our research is that different antioxidant molecules may have a varying impact on AT phenotype. CONCLUSION: NAC and ALA exert different influences on AT, which is reflected in histopathological images, FA transport proteins expression patterns, or even the lipid storage capacity of adipocytes.

The Effect of α-Lipoic Acid on Oxidative Stress in Adipose Tissue of Rats with Obesity-Induced Insulin Resistance.

BACKGROUND/AIMS: Correlation between type 2 diabetes and other abnormalities such as obesity with redox balance disturbance was analyzed in many reports. Nonetheless, antioxidants impact on parameters accompanying these conditions is still unknown. Currently the role of redox imbalance in the adipose tissue has gained a lot of attention. METHODS: We investigated the impact of α-lipoic acid (ALA) on plasma glucose and insulin concentrations, oxidative stress and inflammation parameters in the subcutaneous (SAT) and visceral (VAT) adipose tissue of high fat diet-fed (HFD) rats. Male Wistar rats were randomly divided into three groups (n = 6) - control diet (CTRL), HFD and HFD with α-lipoic acid (HFD+ALA). RESULTS: HFD increased body weight, plasma insulin and glucose as well as leads to oxidative stress parameters in the adipose tissue. ALA supplementation reduced body weight and oxidative stress parameters more effectively in the visceral than subcutaneous adipose tissue of insulin resistant rats. CONCLUSION: Insulin resistance led to increased enzymatic and non-enzymatic antioxidant systems, protein and lipid glycoxidation, nitrosative stress, and selected inflammatory parameters more in VAT than in SAT of insulin resistant rats. Moreover, ALA inhibited HFD consequences mainly in VAT mostly through glutathione (GSH) biosynthesis.

α-Lipoic Acid Strengthens the Antioxidant Barrier and Reduces Oxidative, Nitrosative, and Glycative Damage, as well as Inhibits Inflammation and Apoptosis in the Hypothalamus but Not in the Cerebral Cortex of Insulin-Resistant Rats.

The research determined the role of α-lipoic acid (ALA) in reducing the brain manifestations of insulin resistance. The mechanism of ALA action is mainly based on its ability to "scavenge" oxygen free radicals and stimulate biosynthesis of reduced glutathione (GSH), considered the most critical brain antioxidant. Although the protective effect of ALA is widely documented in various diseases, there are still no studies assessing the influence of ALA on brain metabolism in the context of insulin resistance and type 2 diabetes. The experiment was conducted on male Wistar rats fed a high-fat diet for ten weeks with intragastric administration of ALA for four weeks. We are the first to demonstrate that ALA improves the function of enzymatic and nonenzymatic brain antioxidant systems, but the protective effects of ALA were mainly observed in the hypothalamus of insulin-resistant rats. Indeed, ALA caused a significant increase in superoxide dismutase, catalase, peroxidase, and glutathione reductase activities, as well as GSH concentration and redox potential ([GSH]2/[GSSG]) in the hypothalamus of HFD-fed rats. A consequence of antioxidant barrier enhancement by ALA is the reduction of oxidation, glycation, and nitration of brain proteins, lipids, and DNA. The protective effects of ALA result from hypothalamic activation of the transcription factor Nrf2 and inhibition of NF-κB. In the hypothalamus of insulin-resistant rats, we demonstrated reduced levels of oxidation (AOPP) and glycation (AGE) protein products, 4-hydroxynoneal, 8-isoprostanes, and 3-nitrotyrosine and, in the cerebral cortex, lower levels of 8-hydroxydeoxyguanosine and peroxynitrite. In addition, we demonstrated that ALA decreases levels of proinflammatory TNF-α but also increases the synthesis of anti-inflammatory IL-10 in the hypothalamus of insulin-resistant rats. ALA also prevents neuronal apoptosis, confirming its multidirectional effects within the brain. Interestingly, we have shown no correlation between brain and serum/plasma oxidative stress biomarkers, indicating the different nature of redox imbalance at the central and systemic levels. To summarize, ALA improves antioxidant balance and diminishes oxidative/glycative stress, protein nitrosative damage, inflammation, and apoptosis, mainly in the hypothalamus of insulin-resistant rats. Further studies are needed to determine the molecular mechanism of ALA action within the brain.

NAC Supplementation of Hyperglycemic Rats Prevents the Development of Insulin Resistance and Improves Antioxidant Status but Only Alleviates General and Salivary Gland Oxidative Stress.

Previous studies based on animal models demonstrated that N-acetylcysteine (NAC) prevents oxidative stress and improves salivary gland function when the NAC supplementation starts simultaneously with insulin resistance (IR) induction. This study is the first to evaluate the effect of a 4-week NAC supply on the antioxidant barrier and oxidative stress in Wistar rats after six weeks of high-fat diet (HFD) intake. Redox biomarkers were evaluated in the parotid (PG) and submandibular (SMG) salivary glands and stimulated whole saliva (SWS), as well as in the plasma and serum. We demonstrated that the activity of salivary peroxidase and superoxide dismutase and total antioxidant capacity were significantly higher in PG, SMG, and SWS of IR rats treated with NAC. It appears that in PG and SMG of rats fed an HFD, N-acetylcysteine supplementation abolishes oxidative modifications to proteins (evidenced by decreased content of advanced oxidation protein products (AOPP) and advanced glycation end products (AGE)). Simultaneously, it does not reverse oxidative modifications of lipids (as seen in increased concentration of 8-isoprostanes and 4-hydroxynonenal vs. the control), although it reduces the peroxidation of salivary lipids in relation to the group fed a high-fat diet alone. NAC administration increased protein levels in PG and SMG but did not affect saliva secretion, which was significantly lower compared to the controls. To sum up, the inclusion of NAC supplementation after six weeks of HFD feeding was effective in improving the general and salivary gland antioxidant status. Nevertheless, NAC did not eliminate salivary oxidative stress and only partially prevented salivary gland dysfunction.

High-Sugar Diet Disrupts Hypothalamic but Not Cerebral Cortex Redox Homeostasis.

Despite several reports on the relationship between metabolic and neurodegenerative diseases, the effect of a high-sugar diet (HSD) on brain function is still unknown. Given the crucial role of oxidative stress in the pathogenesis of these disorders, this study was the first to compare the effect of an HSD on the activity of prooxidative enzymes, enzymatic and non-enzymatic antioxidants, and protein oxidative damage in the brain structures regulating energy metabolism (hypothalamus) and cognitive functions (cerebral cortex). Male Wistar rats were randomly divided into two groups (n = 10)-control diet (CD) and high-sugar diet (HSD)-for 8 weeks. We showed a decrease in glutathione peroxidase and superoxide dismutase activity and an increase in catalase activity in the hypothalamus of HSD rats compared to controls. The activity of xanthine oxidase and NADPH oxidase and the contents of oxidation (protein carbonyls), glycoxidation (dityrosine, kynurenine and N-formylkynurenine) and protein glycation products (advanced glycation end products and Amadori products) were significantly higher only in the hypothalamus of the study group. The HSD was also responsible for the disruption of antioxidant systems and oxidative damage to blood proteins, but we did not show any correlation between systemic redox homeostasis and the brain levels. In summary, HSD is responsible for disorders of enzymatic antioxidant defenses only at the central (plasma/serum) and hypothalamic levels but does not affect the cerebral cortex. The hypothalamus is much more sensitive to oxidative damage caused by an HSD than the cerebral cortex.

The Effect of N-Acetylcysteine on Respiratory Enzymes, ADP/ATP Ratio, Glutathione Metabolism, and Nitrosative Stress in the Salivary Gland Mitochondria of Insulin Resistant Rats.

This is the first study to assess the effect of N-acetylcysteine (NAC) on the mitochondrial respiratory system, as well as free radical production, glutathione metabolism, nitrosative stress, and apoptosis in the salivary gland mitochondria of rats with high-fat diet (HFD)-induced insulin resistance (IR). The study was conducted on male Wistar rats divided into four groups of 10 animals each: C (control, rats fed a standard diet containing 10.3% fat), C + NAC (rats fed a standard diet, receiving NAC intragastrically), HFD (rats fed a high-fat diet containing 59.8% fat), and HFD + NAC (rats fed HFD diet, receiving NAC intragastrically). We confirmed that 8 weeks of HFD induces systemic IR as well as disturbances in mitochondrial complexes of the parotid and submandibular glands of rats. NAC supplementation leads to a significant increase in the activity of complex I, II + III and cytochrome c oxidase (COX), and also reduces the ADP/ATP ratio compared to HFD rats. Furthermore, NAC reduces the hydrogen peroxide production/activity of pro-oxidant enzymes, increases the pool of mitochondrial glutathione, and prevents cytokine formation, apoptosis, and nitrosative damage to the mitochondria in both aforementioned salivary glands of HFD rats. To sum up, NAC supplementation enhances energy metabolism in the salivary glands of IR rats, and prevents inflammation, apoptosis, and nitrosative stress.

High Protein Diet Induces Oxidative Stress in Rat Cerebral Cortex and Hypothalamus.

This is the first study to analyze the impact of high protein diet (HPD) on antioxidant defense, redox status, as well as oxidative damage on both a local and systemic level. Male Wistar rats were divided into two equal groups (n = 9): HPD (44% protein) and standard diet (CON; 24.2% protein). After eight weeks, glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), superoxide dismutase-1 (SOD-1), reduced glutathione (GSH), uric acid (UA), total antioxidant (TAC)/oxidant status (TOS) as well as advanced glycation end products (AGE), 4-hydroxynonenal (4-HNE), and malondialdehyde (MDA) were analyzed in the serum/plasma, cerebral cortex, and hypothalamus of HPD and CON rats. HPD resulted in higher UA concentration and activity of GPx and CAT in the hypothalamus, whereas in the cerebral cortex these parameters remained unchanged. A significantly lower GSH content was demonstrated in the plasma and hypothalamus of HPD rats when compared to CON rats. Both brain structures expressed higher content of 4-HNE and MDA, whereas AGE was increased only in the hypothalamus of HPD animals. Despite the enhancement in antioxidant defense in the hypothalamus, this mechanism does not protect the hypothalamus from oxidative damage in rats. Hypothalamus is more susceptible to oxidative stress caused by HPD.

Redox Balance, Antioxidant Defense, and Oxidative Damage in the Hypothalamus and Cerebral Cortex of Rats with High Fat Diet-Induced Insulin Resistance.

Oxidative stress is a key pathogenic factor in both neurogenerative and metabolic diseases. However, its contribution in the brain complications of insulin resistance is still not well understood. Therefore, the aim of this study was the evaluation of redox homeostasis and oxidative damage in the hypothalamus and cerebral cortex of insulin-resistant and control rats. 16 male Wistar rats were divided into two equal groups (n = 8): the control and high fat diet group (HFD). Prooxidant enzymes (xanthine oxidase and NADPH oxidase); enzymatic and nonenzymatic antioxidants [glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), superoxide dismutase-1 (SOD-1), and uric acid (UA)]; and oxidative damage products [advanced glycation end products (AGE), 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), and 8-hydroxy-2'-deoxyguanosine (8-OHdG)] as well as the total antioxidant capacity (TAC), total oxidant status (TOS), oxidative stress index (OSI), and total ferric reducing ability of sample (FRAP) were evaluated in the hypothalamus and cerebral cortex as well as serum/plasma of HFD-fed and control rats. The activity of prooxidant enzymes was significantly increased in the cerebral cortex and hypothalamus of HFD-fed rats vs. control rats. Additionally, we have showed enhanced antioxidant efficiency in the hypothalamus (↑CAT, ↑UA, ↑TAC, and ↑FRAP) and cerebral cortex (↑GPx, ↑CAT, ↑SOD-1, ↑UA, ↑TAC, and ↑FRAP) of HFD-fed rats. All of the oxidative damage markers (AGE, 4-HNE, MDA, 8-OHdG, and OSI) were significantly increased in the cerebral cortex of insulin-resistant rats, while only 4-HNE and MDA were markedly higher in the hypothalamus of the HFD group. Summarizing, the results of our study indicate an adaptive brain response to the increased production of free radicals under insulin resistance conditions. Despite the increase in antioxidative defense systems, this mechanism does not protect both brain structures from oxidative damages. However, the cerebral cortex is more susceptible to oxidative stress caused by HFD.

Whey Protein Concentrate WPC-80 Intensifies Glycoconjugate Catabolism and Induces Oxidative Stress in the Liver of Rats.

The aim of this study was to evaluate the effect of whey protein concentrate (WPC-80) on glycoconjugate catabolism, selected markers of oxidative stress and liver inflammation. The experiment was conducted on male Wistar rats (n = 63). The animals from the study group were administered WPC-80 at a dose of 0.3 or 0.5 g/kg body weight for 7, 14 or 21 days, while rats from the control group received only 0.9% NaCl. In liver homogenates, we assayed the activity of N-acetyl-ß-D-hexosaminidase (HEX), ß-glucuronidase (GLU), ß-galactosidase (GAL), α-mannosidase (MAN), α-fucosidase (FUC), as well as the level of reduced glutathione (GSH), malondialdehyde (MDA), interleukin-1ß (IL-1ß) and transforming growth factor-ß1 (TGF-ß1). A significantly higher activity of HEX, GLU, MAN and FUC were found in the livers of rats receiving WPC-80 compared to controls. Serum ALT and AST were significantly higher in the animals supplemented with WPC-80 at a dose of 0.5 g/kg body weight for 21 days. In the same group of animals, enhanced level of GSH, MDA, IL-1ß and TGF-ß1 were also observed. WPC-80 is responsible for intensive remodelling of liver tissue and induction of oxidative stress especially at a dose of 0.5 g/kg body weight.

Effect of N-Acetylcysteine on Antioxidant Defense, Oxidative Modification, and Salivary Gland Function in a Rat Model of Insulin Resistance.

Oxidative stress plays a crucial role in the salivary gland dysfunction in insulin resistance (IR). It is not surprising that new substances are constantly being sought that will protect against the harmful effects of IR in the oral cavity environment. The purpose of this study was to evaluate the effect of N-acetylcysteine (NAC) on oxidative stress and secretory function of salivary glands in a rat model of insulin resistance. Rats were divided into 4 groups: C-normal diet, C + NAC-normal diet + NAC, HFD-high-fat diet, and HFD + NAC. We have demonstrated that NAC elevated enzymatic (superoxide dismutase, catalase, and peroxidase) and nonenzymatic antioxidants (reduced glutathione (GSH) and total antioxidant capacity (TAS)) in the parotid glands of HFD + NAC rats, while in the submandibular glands increased only GSH and TAS levels. NAC protects against oxidative damage only in the parotid glands and increased stimulated salivary secretion; however, it does not increase the protein secretion in the both salivary glands. Summarizing, NAC supplementation prevents the decrease of stimulated saliva secretion, seen in the HFD rats affected. NAC improves the antioxidative capacity of the both glands and protects against oxidative damage to the parotid glands of IR rats.

Comparison of Selected Parameters of Redox Homeostasis in Patients with Ataxia-Telangiectasia and Nijmegen Breakage Syndrome.

This study compared the antioxidant status and major lipophilic antioxidants in patients with ataxia-telangiectasia (AT) and Nijmegen breakage syndrome (NBS). Total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), and concentrations of coenzyme Q10 (CoQ10) and vitamins A and E were estimated in the plasma of 22 patients with AT, 12 children with NBS, and the healthy controls. In AT patients, TAS (median 261.7 µmol/L) was statistically lower but TOS (496.8 µmol/L) was significantly elevated in comparison with the healthy group (312.7 µmol/L and 311.2 µmol/L, resp.). Tocopherol (0.8 µg/mL) and CoQ10 (0.1 µg/mL) were reduced in AT patients versus control (1.4 µg/mL and 0.3 µg/mL, resp.). NBS patients also displayed statistically lower TAS levels (290.3 µmol/L), while TOS (404.8 µmol/L) was comparable to the controls. We found that in NBS patients retinol concentration (0.1 µg/mL) was highly elevated and CoQ10 (0.1 µg/mL) was significantly lower in comparison with those in the healthy group. Our study confirms disturbances in redox homeostasis in AT and NBS patients and indicates a need for diagnosing oxidative stress in those cases as a potential disease biomarker. Decreased CoQ10 concentration found in NBS and AT indicates a need for possible supplementation.

The importance and perspective of plant-based squalene in cosmetology.

Squalene is a highly unsaturated hydrocarbon from triterpenoid family, discovered as a major component of the liver oil of certain varieties of deep sea sharks. In the interest of protecting biodiversity, raw materials of animal origin must be replaced by alternative sources that respect our environment. Squalene is widely present as a component of the unsaponifiable fraction of vegetable oils (i.e., olive oil, amaranth oil). Amaranth oil seems to be the key source of squalene. Amaranth grains contains 7-7.7% lipids, and these lipids are extremely valuable because of the presence of ingredients like squalene, unsaturated fatty acids, vitamin E as tocopherols, tocotrienols, and phytosterols, which are not seen together in other common oils. In human skin physiology, squalene is not only used as an antioxidant, moisturizer, and material for topically applied vehicle, but is also used in treating skin disorders like seborrheic dermatitis, acne, psoriasis, or atopic dermatitis. Further studies on alternative sources are needed to explore the utility of squalene for treating skin.

Influence of systemic photochemotherapy on regulatory T cells and selected cytokine production in psoriatic patients: a pilot study.

BACKGROUND: Psoriasis is a chronic autoimmune inflammatory disease of the skin with strong genetic and environmental risk factors and is regarded as a Th1 cell-type disease. The aim of our study was to evaluate the effect of one-month PUVA (Psoralen Ultraviolet A) therapy on a regulatory T-cell subpopulation (CD4+CD25+) and the production of some cytokines. MATERIAL/METHODS: The study was performed on the group of 12 patients with severe psoriasis. They were put on PUVA therapy for one month. We analyzed the level of CD4+CD25+ regulatory T cells using a FACSCalibur cytometer and CellQuest Software. The production of IFN-gamma (interferon-gamma), TNF-alpha (tumor necrosis factor alpha), IL (interleukin) -10, IL-5, IL-4, and IL-2 by lymphocytes was estimated by using a CBA system. The control group consisted of 11 healthy volunteers. RESULTS: We found that the production of INF-gamma, TNF-alpha, IL-2, and IL-10 in psoriatic patients before PUVA application increased significantly compared with the control group. In patients after PUVA therapy we observed decreased production of TNF-alpha and a decreased number of CD4+CD25+ cells in the blood compared with the same group of patients before the treatment. CONCLUSIONS: It was demonstrated that systemic PUVA therapy led to a marked reduction in CD4+CD25+ T cells and a change in cytokine production.

Interleukin 4 plasma levels in psoriasis vulgaris patients.

BACKGROUND: Psoriasis is regarded as a Th1-cell type disease. Interleukin-4, a Th2 type cytokine, is diminished in psoriatic skin. It has been postulated that switching the cytokine profile from Th1 to Th2 may be of great help in the treatment of psoriasis. Some recent reports demonstrate a favorable role of IL-4 in the treatment of psoriasis. Therefore we decided to evaluate how IL-4 plasma levels fluctuate in the case of favorable treatment outcome observed in patients with clinically active and stable disease. MATERIAL/METHODS: 17 patients with active psoriasis vulgaris, 17 with stable disease, and 22 age- and sex-matched healthy controls were included in the study. IL- 4 plasma levels were evaluated by the ELISA method twice--before treatment implementation and 4 weeks thereafter. RESULTS: We observed statistically significant higher IL-4 plasma levels in the active psoriasis group both before treatment implementation (1st examination) and after 4 weeks of treatment (2nd examination) compared with both the control group (p<0.001) and the stable psoriasis group (1st examination: p<0.001, 2nd examination: p<0.01). There was no statistically significant difference in IL-4 plasma levels between the stable psoriasis and control groups in both examinations (p>0.05). CONCLUSIONS: Our data seem to support the hypothesis of the existence of immunologically distinct psoriasis subtypes.