Targeted electrochemical reduction of carcinogenic N-nitrosamines from emission control systems within CO2 capture plants.

N-Nitrosamines are one of the environmentally significant byproducts from aqueous amine-based post-combustion carbon capture systems (CCS) due to their potential risk to human health. Safely mitigating nitrosamines before they are emitted from these CO2 capture systems is therefore a key concern before widescale deployment of CCS can be used to address worldwide decarbonization goals. Electrochemical decomposition is one viable route to neutralize these harmful compounds. The circulating emission control waterwash system, commonly installed at the end of the flue gas treatment trains to minimize amine solvent emissions, plays an important role to capture N-nitrosamines and control their emission into the environment. The waterwash solution is the last point where these compounds can be properly neutralized before becoming an environmental hazard. In this study, the decomposition mechanisms of N-nitrosamines in a simulated CCS waterwash with residual alkanolamines was investigated using several laboratory-scale electrolyzers utilizing carbon xerogel (CX) electrodes. H-cell experiments revealed that N-nitrosamines were decomposed through a reduction reaction and are converted into their corresponding secondary amines thereby neutralizing their environmental impact. Batch-cell experiments statistically examined the kinetic models of N-nitrosamine removal by a combined adsorption and decomposition processes. The cathodic reduction of the N-nitrosamines statistically obeyed the first-order reaction model. Finally, a prototype flow-through reactor using an authentic waterwash was used to successfully target and decompose N-nitrosamines to below the detectable level without degrading the amine solvent compounds allowing them to be return to the CCS and lower the system operating costs. The developed electrolyzer was able to efficiently remove greater than 98% of N-nitrosamines from the waterwash solution without producing any additional environmentally harmful compounds and offers an effective and safe route to mitigate these compounds from CO2 capture systems.

The ABCG5 ABCG8 sterol transporter opposes the development of fatty liver disease and loss of glycemic control independently of phytosterol accumulation.

ABCG5 and ABCG8 form a complex (G5G8) that opposes the absorption of plant sterols but is also expressed in liver where it promotes the excretion of cholesterol into bile. Hepatic G5G8 is transcriptionally regulated by a number of factors implicated in the development of insulin resistance and nonalcoholic fatty liver disease. Therefore, we hypothesized that G5G8 may influence the development of diet-induced obesity phenotypes independently of its role in opposing phytosterol absorption. G5G8 knock-out (KO) mice and their wild type (WT) littermates were challenged with a plant sterol-free low fat or high fat (HF) diet. Weight gain and the rise in fasting glucose were accelerated in G5G8 KO mice following HF feeding. HF-fed G5G8 KO mice had increased liver weight, hepatic lipids, and plasma alanine aminotransferase compared with WT controls. Consistent with the development of nonalcoholic fatty liver disease, macrophage infiltration, the number of TUNEL-positive cells, and the expression of proinflammatory cytokines were also increased in G5G8 KO mice. Hepatic lipid accumulation was associated with increased peroxisome proliferator activated receptor γ, CD36, and fatty acid uptake. Phosphorylation of eukaryotic translation initiation factor 2α (eiF2α) and expression of activating transcription factor 4 and tribbles 3 were elevated in HF-fed G5G8 KO mice, a pathway that links the unfolded protein response to the development of insulin resistance through inhibition of protein kinase B (Akt) phosphorylation. Phosphorylation of Akt and insulin receptor was reduced, whereas serine phosphorylation of insulin receptor substrate 1 was elevated.

The absence of ABCD2 sensitizes mice to disruptions in lipid metabolism by dietary erucic acid.

ABCD2 (D2) is a peroxisomal transporter that is highly abundant in adipose tissue and promotes the oxidation of long-chain MUFA. Erucic acid (EA, 22:1ω9) reduces very long chain saturated fatty acids in patients with X-linked adrenoleukodystrophy but promotes dyslipidemia and dilated cardiomyopathy in rats. To determine the role of D2 in the metabolism of EA, we challenged wild-type and D2 deficient mice (D2 KO) with an enriched EA diet. In D2 KO mice, dietary EA resulted in the rapid expansion of adipose tissue, adipocyte hypertrophy, hepatic steatosis, and the loss of glycemic control. However, D2 had no impact on the development of obesity phenotypes in two models of diet-induced obesity. Although there was a significant increase in EA in liver of D2 KO mice, it constituted less than 2% of all fatty acids. Metabolites of EA (20:1, 18:1, and 16:1) were elevated, particularly 18:1, which accounted for 50% of all fatty acids. These data indicate that the failure to metabolize EA in adipose results in hepatic metabolism of EA, disruption of the fatty acid profile, and the development of obesity and reveal an essential role for D2 in the protection from dietary EA.

Pharmacologic properties of polyethylene glycol-modified Bacillus thiaminolyticus thiaminase I enzyme.

We have previously shown that the bacterial enzyme thiaminase 1 has antitumor activity. In an attempt to make thiaminase I a more effective pharmaceutical agent, we have modified it by adding polyethylene glycol (PEG) chains of various lengths. We were surprised to find that 5k-PEGylation eliminated thiaminase cytotoxic activity in all cell lines tested. Both native thiaminase and 5k-PEGylated thiaminase efficiently depleted thiamine from cell culture medium, and both could use intracellular phosphorylated thiamine as substrates. However, native enzyme more effectively depleted thiamine and thiamine diphosphate in RS4 leukemia cell cytosol, and native thiaminase depressed cellular respiration, whereas PEGylated thiaminase did not. Despite the lack of in vitro cytotoxicity, PEGylation markedly increased the in vivo toxicity of the enzyme. Pharmacokinetic studies revealed that the half-life of native thiaminase was 1.5 h compared with 34.4 h for the 5k-PEGylated enzyme. Serum thiamine levels were depleted by both native and 5k-PEGylated enzyme. Despite superior pharmacokinetics, 5k-PEGylated thiaminase showed no antitumor effect against an RS4 leukemia xenograft, in contrast to native thiaminase, which showed antitumor activity. PEGylation of thiaminase I has demonstrated that depression of mitochondrial function contributes, at least in part, to its anticancer activity. PEGylation also enhances plasma retention time, which increased its vivo toxicity and decreased its activity against a leukemia xenograft, the opposite of the desired effects. These studies suggest that the mechanism of anticancer cytotoxicity of thiaminase requires acute depression of cellular respiration, whereas systemic toxicity is related to the duration of extracellular thiamine depletion.

Low-thiamine diet increases mammary tumor latency in FVB/N-Tg(MMTVneu) mice.

We have previously described the down-regulation of thiamine transporter gene expression in breast cancer, and others have shown an epidemiologic relationship between obesity and breast cancer. To further explore the relationship of thiamine, fat, and breast cancer, we exposed FVB/N-Tg(MMTVneu)202Mul/J female mice to four diets that varied in fat and thiamine content (15 mice per group). The high-fat (HF) diet contained 60 % of calories from fat and the normal-fat (NF) diet contained 10 % of calories from fat. The normal-thiamine (NT) diet contained 6 mg thiamine per 4057 kcal and the low-thiamine (LT) diet contained 2 mg thiamine/4057 kcal. Tumor latency was 203 days from date of birth for the HF/NT group, 210 days for the HF/LT group, 225 days for the NF/NT group, and 295 days for the NF/LT group (p = 0.01). The time to endpoint of a mammary tumor volume > 1000 mm3 was 231 days for the HF/NT group, 238 days for the HF/LT group, 257 days for the NF/NT group, and undefined (>310 days) for the NF/LT group (p < 0.001). The high-fat groups were heavier than the normal-fat groups, and the low-thiamine group had a lower serum thiamine level than the normal-thiamine group. There were no differences in the number of pulmonary metastases between groups. This study demonstrates a potential role for dietary thiamine, and an interaction between thiamine and fat, in breast cancer progression.

Linear chain PEGylated recombinant Bacillus thiaminolyticus thiaminase I enzyme has growth inhibitory activity against lymphoid leukemia cell lines.

Cancer cells acquire abnormalities in energy metabolism, collectively known as the Warburg effect, affecting substrate availability of thiamine-dependent enzymes. To investigate a strategy to exploit abnormal cancer-associated metabolism related to thiamine, we tested the cytotoxicity of native Bacillus thiaminolyticus thiaminase I enzyme, which digests thiamine, in the NCI60 cell line drug cytotoxicity screening program and found that leukemia cell lines were among the most sensitive to thiaminase I. We obtained additional lymphoid leukemia cell lines and confirmed that native thiaminase I and linear chain PEGylated thiaminase I enzyme (LCPTE) have cytotoxic activity in these cell lines. In addition, the IC(50) of 3 of the 5 leukemia cell lines (Reh, RS4, and Jurkat) were at least 1,000-fold more sensitive than Molt-4 cells, which in turn, were among the most sensitive in the NCI60 panel. The 3 LCPTE-sensitive leukemia cell lines were also sensitive to removal of thiamine from the medium, thus suggesting the mechanism of action of LCPTE involves extracellular thiamine starvation. Surprisingly, rapamycin showed a protective effect against LCPTE toxicity in the 3 LCPTE-sensitive cell lines but not in the other 2 cell lines, suggesting involvement of an mTOR-dependent pathway. Immunoblot analysis of the LCPTE-sensitive cell lines after LCPTE exposure revealed changes in mTOR pathway phosphorylation. Nude mice bearing RS4 leukemia xenografts showed both tumor growth delay and prolonged survival after a single dose of LCPTE. Therefore, disruption of thiamine-dependent metabolism may be a novel therapeutic approach to target altered energy metabolism in leukemia and other cancers.

ABCD2 is abundant in adipose tissue and opposes the accumulation of dietary erucic acid (C22:1) in fat.

The ATP binding cassette transporter, ABCD2 (D2), is a peroxisomal protein whose mRNA has been detected in the adrenal, brain, liver, and fat. Although the role of this transporter in neural tissues has been studied, its function in adipose tissue remains unexplored. The level of immunoreactive D2 in epididymal fat is >50-fold of that found in brain or adrenal. D2 is highly enriched in adipocytes and is upregulated during adipogenesis but is not essential for adipocyte differentiation or lipid accumulation in day 13.5 mouse embryonic fibroblasts isolated from D2-deficient (D2(-/-)) mice. Although no differences were appreciated in differentiation percentage, total lipid accumulation was greater in D2(-/-) adipocytes compared with the wild type. These results were consistent with in vivo observations in which no significant differences in adiposity or adipocyte diameter between wild-type and D2(-/-) mice were observed. D2(-/-) adipose tissue showed an increase in the abundance of 20:1 and 22:1 fatty acids. When mice were challenged with a diet enriched in erucic acid (22:1), this lipid accumulated in the adipose tissue in a gene-dosage-dependent manner. In conclusion, D2 is a sterol regulatory element binding protein target gene that is highly abundant in fat and opposes the accumulation of dietary lipids generally absent from the triglyceride storage pool within adipose tissue.

Single-drug multiligand conjugates: synthesis and preliminary cytotoxicity evaluation of a paclitaxel-dipeptide "scorpion" molecule.

To improve the targeting properties of receptor-directed drug-peptide conjugates, a multiligand approach was proposed and a model "scorpion" conjugate (6, Figure 1), consisting of two peptide "claws" and a paclitaxel (PTX) "tail", was synthesized. The cell surface receptor-directed peptide used in this single-drug multiligand (SDML) model was a segment of the amphibian peptide bombesin (BBN) which had the Y6Q7W8A9V10G11H12L13M14-NH2 sequence, designated here as BBN[6-14] (2, Figure 2). Due to the lipophilic nature of both PTX and BBN[6-14], compound 6 had a low water solubility. To enhance the solubility, PEG derivatives of this conjugate were prepared with the polymer inserted either in the claws or in the tail regions. In a preliminary random screening, conjugate 6 showed superior cytotoxic activity in several GRPR-positive human cancer cell lines as compared to free PTX and two single-drug single-ligand (SDSL) conjugates. In a receptor blocking experiment, addition of excess unconjugated BBN[6-14] ligand reduced the cytotoxicity of conjugate 6, indicating the receptor-mediated mechanism of drug delivery. The PEG-derived conjugates showed activities which were intermediate between SDSL and the SDML congeners. Also, an increase in the number of the PEG segments lowered cytotoxicity, possibly due to steric hindrance against ligand-receptor binding. Taken together, these results demonstrate the potential of the multiligand approach in the design of receptor-targeting conjugates for tumor-specific drug delivery.