Masamitsu Fukuzawa

Inhibition of development of peripheral neuropathy in streptozotocin-induced diabetic rats with N-acetylcysteine

SummaryN-acetylcysteine (NAC) is a precursor of glutathione (GSH) synthesis, a free radical scavenger and an inhibitor of tumour necrosis factor α (TNF). Because these functions might be beneficial in diabetic complications, in this study we examined whether NAC inhibits peripheral neuropathy. Motor nerve conduction velocity (MNCV) was significantly decreased in streptozotocin-induced-diabetic Wistar rats compared to control rats. Oral administration of NAC reduced the decline of MNCV in diabetic rats. Structural analysis of the sural nerve disclosed significant reduction of fibres undergoing myelin wrinkling and inhibition of myelinated fibre atrophy in NAC-treated diabetic rats. NAC treatment had no effect on blood glucose levels or on the nerve glucose, sorbitol and cAMP contents, whereas it corrected the decreased GSH levels in erythrocytes, the increased lipid peroxide levels in plasma and the increased lipopolysaccharide-induced TNF activity in sera of diabetic rats. Thus, NAC inhibited the development of functional and structural abnormalities of the peripheral nerve in streptozotocin-induced diabetic rats.

Angiotensin converting enzyme inhibitors suppress production of tumor necrosis factor-α in vitro and in vivo

It has been reported that angiotensin converting enzyme (ACE) inhibitors have beneficial effects on insulin resistance and congestive heart failure, in which elevations of serum tumor necrosis factor-α (TNF-α) level have been indicated. Therefore, in this study, we examined effect of ACE inhibitors on TNF-α production both in vitro and in vivo by using human blood mononuclear cells and mice, respectively. LPS (20 μg/ml)-induced in vitro TNF-α production, measured by bioassay and enzyme-linked immunosorbent assay, was significantly inhibited with captopril, delapril and cilazapril in a concentration of 10−3 mol/l. A single, oral administration of captopril, delapril and cilazapril at more than 10-fold doses of common clinical use in man significantly inhibited LPS (2 mg/kg)-induced serum TNF-α activity in Balb/c mice. These results indicate that ACE inhibitors such as captopril, delapril and cilazapril have an inhibitory effect on TNF-α production not only in vitro as previously reported, but also in vivo, although relatively high concentrations and large doses were required in this study.

Inhibitory effect of troglitazone on diabetic neuropathy in streptozotocin-induced diabetic rats.

Summary Free-radical scavengers and inhibitors of tumour necrosis factor-α (TNF-α) such as N-acetylcysteine and pentoxifylline have been shown to inhibit the development of peripheral neuropathy in streptozotocin(STZ)-induced diabetic rats. In this study we examined the effect of troglitazone, an anti-diabetic thiazolidinedione, on diabetic neuropathy, since it also is a free-radical scavenger and a TNF-α inhibitor. Rats were fed powder chow mixed with troglitazone at 0.5 % and 0.125 % ad libitum. Although blood glucose concentrations were remarkably higher and body weight lower in diabetic than in nondiabetic rats, troglitazone had no effect on these throughout the 24-week experiment. Serum lipoperoxide concentrations, tibial nerve lipoperoxide content and serum TNF-α activity induced by lipopolysaccharide was increased in diabetic rats, but inhibited in troglitazone-treated rats. Motor nerve conduction velocity (MNCV) of the tibial nerve slowed in diabetic rats, compared with that in nondiabetic rats. On the other hand, the slowed MNCV was (p < 0.05–0.01) inhibited after weeks 12 and 16 of the experiment in diabetic rats treated with high and low doses of troglitazone, respectively. Morphometric analysis showed that troglitazone suppressed the decrease of the myelinated fibre area (p < 0.05), axon/myelin ratio (p < 0.01) and fascicular area (p < 0.05) and suppressed the increase of myelinated fibre density (p < 0.001) in diabetic rats. These results indicate that troglitazone has a beneficial effect on peripheral neuropathy in STZ-induced diabetic rats irrespective of blood glucose concentrations. [Diabetologia (1998) 41: 1321–1326]

Inhibition of tumor necrosis factor-α with anti-diabetic agents

It has recently been indicated that tumor necrosis factor-alpha (TNF-alpha) production is increased under chronic hyperglycemia and TNF-alpha has harmful effects on insulin sensitivity and possibly on chronic diabetic complications. Therefore it will be favorable for diabetes treatment if anti-diabetic agents also have anti-TNF-alpha activities. In this study, we have investigated effects of hypoglycemic sulfonylureas (gliclazide and glibenclamide) and a thiazolidinedione (troglitazone) on lipopolysaccharide-induced TNF-alpha production, which was evaluated by immunoassay and bioassay, in vivo using mice and partly in vitro using human peripheral blood mononuclear cells. Gliclazide significantly inhibited TNF-alpha production in vivo and also in vitro at a concentration of 10(-3) mol/l. However, glibenclamide had neither effect on TNF-alpha production nor action. On the other hand, troglitazone inhibited action rather than production of TNF-alpha in vivo. In vitro troglitazone (10(-4) mol/l) significantly reduced cytolytic activity of TNF-alpha against LM cells. These results indicate that gliclazide and troglitazone have inhibitory effect on TNF-alpha.

Inhibitory effect of nicotinamide on in vitro and in vivo production of tumor necrosis factor-α

Nicotinamide, a pellagra-preventive factor, has multiple functions such as inhibition of poly-ADP-ribose synthetase, inhibition of inducible nitric oxide synthase, free radical scavenging and suppression of major histocompatibility complex class II expression and ICAM-1 expression on endothelial cells. In addition to these, we have found an inhibitory effect of nicotinamide on production of tumor necrosis factor-alpha (TNF-alpha) in vitro and in vivo. Lipopolysaccharide (LPS)-induced in vitro TNF-alpha production by human peripheral blood mononuclear cells, measured by enzyme-linked immunosorbent assay (ELISA), was significantly inhibited with more than 1 x 10(-3) mol/l of nicotinamide, while interleukin-1-beta was not inhibited and interleukin-6 was slightly inhibited even with 10(-2) mol/l. Oral administration of nicotinamide with more than 62.5 mg/kg also significantly inhibited LPS-induced serum TNF-alpha production measured by ELISA and bioassay in Balb/c mice. Thus, nicotinamide has an inhibitory effect on TNF-alpha production that may be beneficial to TNF-alpha-mediated diseases.

Modulation of tumor necrosis factor-α production with anti-hypertensive drugs

Abstract It is well known that some anti-hypertensive drugs affect insulin sensitivity and that tumor necrosis factor-α (TNF-α) is a mediator of obesity-associated insulin resistance. In this study, we have investigated the effect of anti-hypertensive drugs, calcium (Ca) channel blockers (amlodipine, manidipine and nicardipine), an α1-blocker (doxazosin), a β1-blocker (metoprolol), and a thiazide diuretic (hydrochlorothiazide), on lipopolysaccharide (LPS)-induced TNF-α production. TNF-α production, measured with a bioassay and an immunoassay, was evaluated both in vivo and in vitro, by utilizing mice and a human peripheral blood mononuclear cell culture, respectively. Nicardipine, or amlodipine, manidipine and doxazosin significantly inhibited TNF-α production in mice at doses more than one or ten times higher than those used clinically, respectively. On the other hand, metoprolol increased TNF-α production at doses of more than 10 times those used clinically, whereas hydrochlorothiazide did not alter production of the cytokine. The in vivo effects of these drugs were not necessary parallel to the in vitro effects. Because high doses of these drugs in mice correspond to clinical doses and effects in human, these actions may be related to beneficial and/or harmful effects of these drugs on TNF-α mediated diseases, including insulin resistance.