Biosynthesis of long-chain alcohols by developing and regenerating rat sciatic nerve

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

My Journey in Academia as a Lipid Biochemist

An overview of Prof. Viswanathan Natarajan's journey in academia as a mentor, teacher, and lipid scientist for nearly 50 years is presented. As a graduate student, Dr. Natarajan interrogated biosynthesis and catabolism of phospholipids in the developing brain; however, in the last five decades, he has been investigating the role of sphingolipids and sphingolipid-metabolizing enzymes in pulmonary endothelial cells, epithelial cells, and fibroblasts under normal conditions and during various lung pathologies such as sepsis, asthma, pulmonary hypertension, idiopathic pulmonary fibrosis, bronchopulmonary dysplasia, and lung cancer. His recent work on sphingosine-1-phosphate and lysophosphatidic acid metabolism in pre-clinical animal models has identified small molecule inhibitors in the signaling pathways that could have therapeutic potential in ameliorating pulmonary fibrosis, hypoxia-induced pulmonary hypertension, lung cancer, and bronchopulmonary dysplasia. Future research in bioactive lipids in combination with OMICS should unravel the importance of various lipid mediators as modulators of cell function under normal and pathological conditions.

Pharmacokinetics and metabolism of14C-1,3-dichloropropene in the Fischer 344 rat and the B6C3F1mouse

1. 14C-1,3-dichloropropene (14C-DCP) is rapidly absorbed and eliminated in both the male F344 rat and B6C3F1 mouse following oral administration of 1 or 50 mg kg(-1) (rat) or 1 or 100 mg kg(-1) (mouse). 2. It is extensively metabolized in both species. Urinary excretion was the major route of elimination, accounting for 50.9-61.3 and 62.5-78.6% of the administered dose in rat and mouse, respectively. 3. Urinary elimination half-lives ranged from 5 to 6 h (rat) and from 7 to 10 h (mouse). Elimination via faeces or as 14CO2 accounted for 14.5-20.5 and 13.7-17.6% of the administered dose, respectively. 4. Metabolites arising from glutathione conjugation account for 36-55 and 48-50% of the administered dose in excreted from rats and mice, respectively. Hydrolysis of the 3-chloro moiety of DCP accounted for 24-37 and 29% of the dose administered to rats and mice, respectively. Two novel dimercapturic acid conjugates were also identified at low levels that might arise via initial hydrolysis of DCP or of epoxidation of DCP-glutathione conjugate or of DCP itself. Structural confirmation of these dimercapturates was obtained via analysis of deuterium retention from D4-DCP in the male F344 rat. 5. Only quantitative differences are seen between the overall metabolic profile of DCP in these two species.

Effects of long-chain fatty alcohol on peripheral nerve conduction and bladder function in diabetic rats

Diabetic cystopathy as manifested by an enlarged bladder is mainly caused by peripheral neuropathy. Long-chain fatty alcohol, which has been isolated from the Far-Eastern traditional medicinal plant, Hygrophilia erecta, Hochr., has been found to possess some neurotrophic activities on the central neuron. Cyclohexenonic long-chain fatty alcohol (FA) used in this study were synthesized in order to improve the efficiency of the molecules. The effects of this compound on peripheral nerves, however, have not yet been studied. To get more information, we evaluated the effects of this compound on peripheral nerves in streptozotocin-induced diabetic rats in terms of nerve conduction velocity and bladder function. Three experiments were performed 8 weeks after the administration of streptozotocin to 8-week-old rats: (i) motor sciatic nerve conduction (MNCV), (ii) monitoring micturition behavior in the metabolic cage, and (iii) cystometrogram under urethane anesthesia (CMG). Half of the diabetic rats were treated with FA (8 mg/kg/day, i.p.). The difference in MNCV between control rats (49.0 +/- 2.2 m/s) and untreated diabetic rats (42.4 +/- 0.5 m/s) after 8 weeks reached significance (p = 0.0183). FA-administrated diabetic rats showed an improved MNCV (45.8 +/- 1.2 m/s). We also identified a significant improvement of bladder function in these animals. The diabetic rats had a much higher maximal micturition volume per 24 hours (4.9 +/- 0.4 ml) than control animals (1.5 +/- 0.1 ml). However, the diabetic rats treated with FA had a maximal micturition volume of only 3.7 +/- 0.3 ml. Likewise, the diabetic rats had a CMG bladder capacity of 0.90 +/- 0.14 ml while the diabetic rats treated with FA had a capacity of 0.54 +/- 0.07 ml. These results indicate that cyclohexenonic long-chain fatty alcohol has a beneficial effect on peripheral neuropathy and cystopathy in streptozotocin-induced diabetic rats.

Neurotrophic activity of 2,4,4-trimethyl-3-(15-hydroxypentadecyl)-2-cyclohexen-1-one in cultured central nervous system neurons

Endogenous neurotrophic factors are essential for the development and maintenance of the nervous system. This suggests their potential utilization as therapeutic agents for neurodegenerative diseases. However, the clinical use of these proteic factors is still restricted, and brings about undesirable consequences, including adverse side effects, and bioavailability and stability difficulties. Therefore, the development of low-molecular weight, non-proteic synthetic compounds with neurotrophic properties appears as a promising approach. The aim of this study was to explore the biological activity of 2,4,4-trimethyl-3-(15-hydroxypentadecyl)-2-cyclohexen-1-one (tCFA15), a trimethyl cyclohexenonic long-chain fatty alcohol. To this end, neurons from fetal rat cerebral hemispheres were cultured in the presence of increasing doses of tCFA15 ranging from 0.1 to 1000 nM. Quantification of cell numbers after 48-h culture showed that 100 nM tCFA15 induced a significant increase in the number of surviving cells. Measurement of total neurite length in microtubule-associated protein 2-positive cells also revealed a stimulatory effect in a wider range of concentrations. The extent of this neuritogenic action was similar to that induced by dibutyryl-cyclic AMP, a well-known neurite outgrowth stimulator, but used at much higher concentration (1 mM). Analysis of structure-activity relationships with different tCFA15 analogs and derivatives corroborated the neurotrophic activity. Taken together, these findings provide strong evidence that tCFA15 exhibits neurotrophic properties in vitro.

The neurotrophic factor, n-hexacosanol, reduces the neuronal damage induced by the neurotoxin, kainic acid

The long-chain fatty alcohol, n-hexacosanol, has been shown to possess neurotrophic properties in vitro on rat CNS cultures (Borg et al., 1987) and to promote the survival of septal cholinergic neurons after experimental axotomy (Borg et al., 1990). Long-chain alcohols have also been shown to be synthesized and metabolised by rat brain during development (Bishop and Hayra, 1981; Natarajan et al., 1984). The present study was undertaken in order to find out if a nonproteic neurotrophic factor like n-hexacosanol may be able to reduce the neuronal damages induced by the excitatory amino acid, kainic acid. When administered chronically by intraperitineal injection, hexacosanol (1 mg/kg) protected the pyramidal neurons of the hippocampus from the neurotoxic degeneration induced by an intracerebroventricular infusion of kainic acid in rats; the extent of the damage was limited to a small part of the CA3 region. Morphometric analysis showed that 72% of the neurons that would have died following kainic acid injection were spared by hexacosanol. Moreover the increased locomotor activity induced by the neurotoxin was also inhibited by hexacosanol and the behavioral effect was statistically correlated to the extent of neuronal loss. The present study suggests a possible role for nonproteic neurotrophic compounds against neurotoxic damages on central neurons. Moreover the peripheral administration of hexacosanol may lead to a significant breakthrough in the treatment of exicotoxin-related human diseases.

Peripheral administration of a long-chain fatty alcohol promotes septal cholinergic neurons survival after fimbria-fornix transection

Peripherally administered n-hexacosanol, a long-chain fatty alcohol, strongly attenuated the degeneration of cholinergic neurons in the medial septum and the vertical limb of the diagonal band of Broca following transection of their dorsal projection to the hippocampus by unilateral fimbria-fornix aspiration. The maintenance of AChE-positive neurons was particularly striking in the vertical limb of the diagonal band of Broca, where 83% of the neurons survived after two weeks of n-hexacosanol treatment compared to 51% in the non-treated animals. This compound has already been found to possess some neurotrophic activities on cultured neurons from rat cerebral cortex. But the present study is the first report of an in vivo neurotrophic influence exerted by an exogenously administered long-chain fatty alcohol. The low dosage needed and the peripheral administration of this compound may be of great advantage in the reduction of cell loss in some neurodegenerative disorders like Alzheimer's disease or stroke.

Participation of microsomal aldehyde reductase in long-chain fatty alcohol synthesis in the rat brain

The participation of microsomal aldehyde reductase in long-chain fatty alcohol synthesis in the rat brain was examined. A reaction mixture of [1-14C]hexadecanoic acid with brain microsomes and NADPH formed two radioactive products having the same mobilities as pure hexadecanal (RF 0.61) and hexadecanol (RF 0.22), respectively, on TLC plates. The product of the RF 0.61 spot was further identified as hexadecanal using gas-liquid chromatography after methylation and TLC of its reduced product with LiAlH4 and semicarbazide. The ratio of hexadecanal to hexadecanol varied from 0.4 to 1.2 under the present experimental conditions. When solubilized rat brain microsomes were applied to a Sepharose 4B column coupled with the rabbit antibody raised against rat liver microsomal NADPH-cytochrome-c reductase, which reacts with aldehyde reductase from rat brain, the eluted fraction ceased to form [14C]hexadecanol but continued to form [14C]hexadecanal from [14C]hexadecanoic acid. These results strongly indicate that hexadecanal is the intermediate in the synthesis of hexadecanol from hexadecanoic acid in rat brain microsomes with the participation of microsomal aldehyde reductase.

Inositol phospholipid hydrolysis by rat sciatic nerve phospholipase C

Rat sciatic nerve cytosol contains a phosphodiesterase of the phospholipase C type that catalyzes the hydrolysis of inositol phospholipids, with preferences of phosphatidylinositol 4'-phosphate (PIP) greater than phosphatidylinositol (PI) much greater than phosphatidylinositol 4',5'-bisphosphate (PIP2), at a pH optimum of 5.5-6.0 and at maximum rates of 55, 13, and 0.7 nmol/min/mg protein, respectively. Analysis of reaction products by TLC and formate exchange chromatography shows that inositol 1,2-cyclic phosphate (83%) and diacylglycerol are the major products of PI hydrolysis. [32P]-PIP hydrolysis yields inositol bisphosphate, inositol phosphate, and inorganic phosphate, indicating the presence of phosphodiesterase, phosphomonoesterase, and/or inositol phosphate phosphatase activities in nerve cytosol. Phosphodiesterase activity is Ca2+-dependent and completely inhibited by EGTA, but phosphomonoesterase activity is independent of divalent cations or chelating agents. Phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) inhibit PI hydrolysis. They stimulate PIP and PIP2 hydrolysis up to equimolar concentrations, but are inhibitory at higher concentrations. Both diacylglycerols and free fatty acids stimulate PI hydrolysis and counteract its inhibition by PC and lysoPC. PIP2 is a poor substrate for the cytosolic phospholipase C and strongly inhibits hydrolysis of PI. However, it enhances PIP hydrolysis up to an equimolar concentration.

Neurotrophic effect of naturally occurring long-chain fatty alcohols on cultured CNS neurons

A long-chain fatty alcohol,n-hexacosanol, that we have isolated from the Far-Eastern traditional medicinal plant, Hygrophila erecta, Hochr., is shown to promote the maturation of central neurons. Added at 500 nM to fetal rat brain neurons in culture, it increased both neurite outgrowth by a factor of 4-6 and the number of collaterals, especially in multipolar neurons. The biochemical differentiation of cultured neurons was also strikingly enhanced by this compound: it increased the protein content and almost doubled the activities of two neuron-specific enzymes, phosphate-activated glutaminase and neuron-specific enolase, by 92 and 78%, respectively. Extensive studies with several synthetic long-chain fatty alcohols showed that the neurotrophic activity was maximal for n-hexacosanol. It is suggested that some long-chain fatty alcohols with an appropriate length of hydrocarbon chain might play an important role in central neuron development.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)