Co-combustion of agricultural residues with coal in a fluidized bed combustor.

Power generation from biomass is an attractive technology that utilizes agricultural residual waste. In order to explain the behavior of biomass-fired fluidized bed incinerator, biomass sources from agricultural residues (rice husk and palm kernel) were co-fired with coal in a 0.15m diameter and 2.3m high fluidized bed combustor. The combustion efficiency and carbon monoxide emissions were studied and compared with those for pure coal combustion. Co-combustion of a mixture of biomass with coal in a fluidized bed combustor designed for coal combustion increased combustion efficiency up to 20% depending upon excess air levels. Observed carbon monoxide levels fluctuated between 200 and 900 ppm with the addition of coal. It is evident from this research that efficient co-firing of biomass with coal can be achieved with minimal modifications to existing coal-fired boilers.

The peroxisome proliferators are hepatocyte mitogens in chemically-defined media: glucocorticoid-induced PPAR alpha is linked to peroxisome proliferator mitogenesis.

Peroxisome proliferator-induced mitogenesis is believed to play a role in hepatocarcinogenesis, but it has not been possible to demonstrate high level induction of DNA synthesis by peroxisome proliferators in cultured hepatocytes. We now show that four structurally dissimilar peroxisome proliferators (methylclofenapate, Wy-14 643, tetradecyl-3-thia acetic acid and clofibrate) cause high level induction of DNA synthesis in primary cultures of rat hepatocytes, routinely 7-9 fold above control, with up to 29% of cells undergoing S-phase. Peroxisome proliferators induce DNA synthesis rapidly, with maximal response 24 h after dosing [compared with 48 h for epidermal growth factor (EGF)]; indeed, peroxisome proliferators were mitogenic in a chemically defined medium, i.e. with no added exogenous growth factors. EGF-treated hepatocytes that had undergone DNA synthesis comprised 23% binucleated cells, whereas hepatocytes induced into S-phase by peroxisome proliferators contained only 3% binucleated cells, demonstrating a distinct response of hepatocytes to peroxisome proliferators and EGF. The presence of a glucocorticoid was essential for peroxisome proliferator-induced DNA synthesis, but not for EGF-induced DNA synthesis, demonstrating that the requirement for glucocorticoids is selective for peroxisome proliferators. Hydrocortisone was shown to induce the expression of peroxisome proliferator activated receptor-alpha (PPAR alpha), and we propose that it is the glucocorticoid-induced expression of PPAR alpha that is essential for peroxisome proliferator mitogenesis. This in vitro system provides a powerful tool for investigating the mechanism and role of peroxisome proliferator-induced mitogenesis in liver growth and carcinogenesis.

Molecular basis of non-responsiveness to peroxisome proliferators: the guinea-pig PPARalpha is functional and mediates peroxisome proliferator-induced hypolipidaemia.

The guinea pig does not undergo peroxisome proliferation in response to peroxisome proliferators, in contrast with other rodents. To understand the molecular basis of this phenotype, the peroxisome proliferator activated receptor alpha (PPARalpha) from guinea-pig liver was cloned; it encodes a protein of 467 amino acid residues that is similar to rodent and human PPARalpha. The guinea-pig PPARalpha showed a high substitution rate: maximum likelihood analysis was consistent with rodent monophyly, but could not exclude rodent polyphyly (P approximately 0.06). The guinea-pig PPARalpha cDNA was expressed in 293 cells and mediated the induction of the luciferase reporter gene by the peroxisome proliferator, Wy-14,643, dependent on the presence of a peroxisome proliferator response element. Moreover the PPARalpha RNA and protein were expressed in guinea-pig liver, although at lower levels than in a species which is responsive to peroxisome proliferators, the mouse. To determine whether the guinea-pig PPARalpha mediated any physiological effects, guinea pigs were exposed to two selective PPARalpha agonists, Wy-14, 643 and methylclofenapate; both compounds induced hypolipidaemia. Thus the guinea pig is a useful model for human responses to peroxisome proliferators.

A novel murine P-450 gene, Cyp4a14, is part of a cluster of Cyp4a and Cyp4b, but not of CYP4F, genes in mouse and humans.

Genomic clones for Cyp4a12 and a novel member of the murine Cyp4a gene family were isolated. The novel gene, designated Cyp4a14, has a GC rich sequence immediately 5' of the transcription start site, and is similar to the rat CYP4A2 and CYP4A3 genes. The Cyp4a14 gene spans approximately 13 kb, and contains 12 exons; sequence similarity to the rat CYP4A2 gene sequence falls off 300 bp upstream from the start site. In view of the known sex-specific expression of the rat CYP4A2 gene, the expression and inducibility of Cyp4a14 was examined. The gene was highly inducible in the liver when mice were treated with the peroxisome proliferator, methylclofenapate; induction levels were low in control animals and no sex differences in expression were observed. By contrast, the Cyp4a12 RNA was highly expressed in liver and kidney of control male mice but was expressed at very low levels in liver and kidney of female mice. Testosterone treatment increased the level of this RNA in female liver slightly, and to a greater extent in the kidney of female mice. In agreement with studies on the cognate RNA, expression of Cyp4a12 protein was male-specific in the liver of control mice and extremely high inducibility of Cyp4a10 protein, with no sex differences, was also demonstrated. In view of the overlapping patterns of inducibility of the three Cyp4a genes, we investigated whether the three genes were co-localized in the genome. Two overlapping yeast artificial chromosome (YAC) clones were isolated, and the three Cyp4a genes were shown to be present on a single YAC of 220 kb. The Cyp4a genes are adjacent to the Cyp4b1 gene, with Cyp4a12 most distant from Cyp4b1. The clustering of these two gene subfamilies in the mouse was replicated in the human, where the CYPA411 and CYP4B1 genes were present in a single YAC clone of 440 kb. However, the human CYP4F2 gene was mapped to chromosome 19. Phylogenetic analysis of the CYP4 gene families demonstrated that CYP4A and CYP4B are more closely related than CYP4F.

Chromosomal localisation, inducibility, tissue-specific expression and strain differences in three murine peroxisome-proliferator-activated-receptor genes.

Three murine peroxisome-proliferator-activated-receptor (PPAR) genes were localised to chromosome 15 (PPAR alpha), chromosome 17 (PPAR beta) and chromosome 6 (PPAR gamma). The expression of the three PPAR RNAs was determined using a specific RNase protection assay. In liver RNA, PPAR alpha was expressed at the highest level, with 20-fold lower levels of PPAR beta, and very low levels of PPAR gamma. The three PPAR RNAs showed no sex-specific differences in expression, and the levels of these transcripts were unaffected by treatment of mice with testosterone or the potent peroxisome proliferator, methylclofenapate. In agreement with this data, the level of PPAR alpha protein in liver was unchanged after treatment of mice with methylclofenapate. Investigation of the tissue-specific distribution revealed that the PPAR alpha RNA was expressed at highest levels in liver, to moderate levels in kidney and brown adipose tissue, and at low levels elsewhere. PPAR beta was expressed at moderate levels in liver, and lower levels in other tissues, including brown adipose tissue. In contrast, PPAR gamma RNA was expressed at low levels in liver or epididymal white adipose tissue and at very low levels elsewhere, but was expressed at high levels in brown adipose tissue. The tissue distribution of these receptors suggests an important role in lipid metabolism and toxicity for individual members of the PPAR family. The expression of PPAR alpha and PPAR beta RNAs was examined in 13 strains of mice, and the levels of expression varied within a fourfold range. Polymorphism in the size of PPAR alpha RNA from Swiss-Webster mice was detected, and shown to be due to a 2-bp mutation in the 3' non-coding region of PPAR alpha in Swiss Webster mice.