Enhancement of mitogen-induced lymphocyte proliferation by some inhibitors of alkaline phosphatase and diamine oxidase

We selected various compounds [bromolevamisole, levamisole, cimetidine, L-homoarginine, 2,3,5,6-tetrahydroimidazo-(2,1-b)thiazole (IT), imidazole, theophylline] previously reported as inhibitors of alkaline phosphatase (ALP) and/or diamine oxidase (DAO) and studied their activity on concanavalin A (ConA)-induced mouse spleen cell lymphocyte proliferation. According to the Ki values, the decreasing order of potency for ALP inhibition was: bromolevamisole, levamisole, theophylline, cimetidine, IT, imidazole and L-homoarginine. The order of potency was different for DAO inhibition. Cimetidine was the most potent inhibitor of DAO, followed by bromolevamisole, levamisole, IT, imidazole and L-homoarginine. Theophylline had no inhibitory effect on DAO. We show that these compounds, except theophylline, enhance ConA-induced lymphocyte proliferation. Similarly, all the compounds except imidazole and theophylline, significantly inhibited ALP at concentrations which enhanced lymphocyte proliferation as measured by (3H)-thymidine uptake. DAO inhibition correlated with DNA synthesis only for IT and cimetidine. These observations suggest that ALP and DAO play a negative role in the proliferation process; however, the degree of enhancement of ConA-induced proliferation did not correlate strictly with the degree of ALP and DAO inhibition.     

Therapeutic effect of cimetidine on acetaminophen-induced hepatotoxicity in rabbits

Acetaminophen is an analgesic and antipyretic drug that may cause hepatic toxicity in humans and experimental animals. Cimetidine is an H₂ blocker used for suppression of gastric acid secretion. One of the side effects of cimetidine is blockade of the cytochrome P-450 enzyme system which results in increased half-life of some drug. In this study, 120 female rabbits, randomized into 12 groups (three control and nine test groups), were used. Acetaminophen, 3.24 g/kg, in suspension form as the LD₅₀, was administered orally to induce liver necrosis. Cimetidine (40 mg/kg) was administered intravenously at 0, 2, and 4 h after administration of acetaminophen. Some treatment groups received cimetidine in two equal divided doses—20 mg/kg cimetidine was administered at 2 and 12 h, 2 and 24 h, 4 and 12 h, and 4 and 24 h after administration of acetaminophen. Blood samples were collected at 0, 12, 24, and 36 h after induction of acetaminophen toxicity. Alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, bilirubin, and arginase were measured in all groups and were found to be increased in acetaminophen control group and some treatment groups (p < 0.05). Results showed that the best treatment effect of cimetidine could be obtained with whole dose of cimetidine administration and 2 h after acetaminophen intake.     

Comparative effects of antacids, cimetidine and enteric coating on the therapeutic response to oral enzymes in severe pancreatic insufficiency.

To provide a rational basis for pancreatic enzyme replacement therapy, we evaluated, in six patients with advanced pancreatic insufficiency, the effects of various treatment regimens on fecal fat and nitrogen balance and on duodenal recovery of ingested pancreatic enzymes after a solid test meal. The combination of cimetidine (an H2-receptor antagonist) and pancreatin, each given by mouth, produced significantly higher postprandial duodenal recoveries and concentrations of trypsin and lipase (P less than 0.05). Steatorrhea was reduced in all patients and abolished in four of the six. In the dosages used, neither enteric-coated enzymes nor supplemental neutralizing antacids were more effective than pancreatin alone in decreasing steatorrhea or improving duodenal enzyme delivery. Cimetidine may be a useful adjunct to oral pancreatic extract therapy in some patients with severe pancreatic insufficiency who fail to respond to pancreatic enzyme replacement alone.     

The effect of cimetidine on the immediate cutaneous response to allergens.

The effects of an H2 antagonist cimetidine on the immediate cutaneous response to timothy or ragweed extract were evaluated. Cimetidine had no effect on the immediate cutaneous response to either allergen. These findings suggest that cimetidine need not be discontinued prior to allergy skin testing.     

Antimetastatic effect of cimetidine on mice bearing a C3H mouse mammary adenocarcinoma: survival and lymphocyte function studies

It has been reported that treatment with cimetidine, a histamine H₂-receptor antagonist, increased survival and decreased the number of lung metastases in mice bearing the Lewis Lung carcinoma [29]. It was suggested that this effect was due to the ability of cimetidine to block histamine activation of suppressor lymphocytes and hence allow host defence mechanisms to inhibit tumour growth. In the present studies, C3H/He mice were implanted with a C3H mouse mammary adenocarcinoma on Day 0. This tumour metastasizes to the lungs in 30–50 days. Primary tumours were ablated with X-rays when they had grown to about 0·2g and animals were given drinking water with or without cimetidine (10 mg ml^–1) until the end of the experiment. Cimetidine reduced the number of mice dying from metastatic disease from 7/15 (controls) to 3/13. Cimetidine treatment also prolonged survival of mice that did succumb to metastatic disease by about 12 days. The response of spleen lymphocytes to the mitogens phytohaemagglutinin and lipopolysaccharide was assessed in vitro by uptake of ³H-thymidine 0, 16, 45 and 58 days after tumour implantation. Lymphocyte responsiveness was depressed by tumour burden. The influence of cimetidine treatment was equivocal being dependent upon time after tumour implantation and dose of mitogen. In this mouse-tumour system, the mechanism of the antimetastic effect of cimetidine is different from that previously suggested [29].     

Effect of low dose of cimetidine on gastric potential difference and acetylsalicylic acid-induced change

Summary Cimetidine in a low dose of 10 mg given intravenously increases significantly the gastric potential difference (GPD) without any inhibitory effect on gastric acid secretion. The increase of GPD after 200 mg cimetidine is higher than after 10 mg. While the high dose of cimetidine prevents the acetylsalicyclic acid (ASA)-induced GPD drop, cimetidine in a dose of 10 mg is not able to protect this change. Nevertheless the low dose of cimetidine may have a clinical significance and should be evaluated by clinical studies.Dedicated to Prof. Dr. G.A. Martini, Marburg, on the occasion of his 65th birthday     

Cimetidine inhibits the adhesion of gastric cancer cells expressing high levels of sialyl Lewis x in human vascular endothelial cells by blocking E-selectin expression

Cimetidine has been shown to have anti-metastatic activity and improves the survival of patients with colorectal cancer. One hypothesis is its modulation of the expression of the cell adhesion molecule by target organ endothelial cells. Because of the inconclusive results in clinical trials of gastric cancer, we investigated the effects of cimetidine on the adhesion of gastric cancer cells to activated endothelial cells and on the expression of some cell adhesion molecules. Human endothelial cells were pre-incubated with cimetidine for 6 h, incubated with the cytokine tumor necrosis factor for 4?h, and the endothelial surface expression of E-selectin was evaluated by flow cytometry, immunostaining and ELISA. Further, we investigated E-selectin mRNA expression by RT-PCR. Three gastric cancer cell lines (SGC-7901, MGC-803, BGC-823) and a normal gastric epithelial cell line, GES-1, were studied for the surface expression of sialyl Lewis x by flow cytometry and immunostaining. Adherence of CFSE-labeled gastric cancer cells and GES-1 cells to endothelial cell monolayers was determined. Cimetidine significantly reduced E-selectin expression of activated endothelial cells, but did not influence E-selectin expression at the mRNA level. Three gastric cancer cell lines expressed high levels of sialyl Lewis x, whereas GES-1 did not. Cimetidine also significantly decreased gastric cancer cell adherence to stimulated endothelial cells. The inhibition of E-selectin expression corresponded to the reduction of tumor cell adherence. The effects of cimetidine on tumor adhesion were almost nullified by pre-incubation with E-selectin and sialyl Lewis x antibody. Furthermore, there was no significant change of GES-1 adherence to endothelial cells by TNF-α, cimetidine, E-selectin and sialyl Lewis x antibody. The inhibiton of gastric cancer cell adherence to cytokine-stimulated endothelial cells treated with cimetidine appears to result from blocking endothelial E-selectin expression. These data support the hypothesis that cimetidine may exert its anti-metastatic effects in gastric cancer, in part, by inhibiting E-selectin/sialyl Lewis x-mediated adherence of gastric cancer cells to endothelial cells in the metastasis target organs.     

Investigations into the reported ability of cimetidine to initiate UDS in rat hepatocyte primary cultures

Cimetidine is widely prescribed as a palliative or cure for gastric disorders in man. It is known to be noncarcinogenic to rodents and has been shown to be inactive in a wide range of in vitro and in vivo genotoxicity assays. It was therefore of concern when an injectable formulation of this drug (Cimetex) was reported to initiate UDS in cultured primary rat hepatocytes [Martelli et al, 1983]. We have confirmed the ability of Cimetex to elicit UDS in primary hepatocytes and established that cimetidine itself is inactive. These data indicate that it is not cimetidine per se, but rather its protonated formulation which is responsible for the activity. These observations pose fundamental questions regarding the validity of the UDS end-point when testing salts in vitro, rather than presenting a challenge to the nongenotoxic status of cimetidine.     

Phagocytic and bactericidal activities of neutrophils in duodenal ulcer patients during cimetidine treatment

Phagocytic and bactericidal activities of neutrophils relative to Staphylococcus aureus 209 P strain were studied in 16 duodenal ulcer patients who were intravenously administered cimetidine in doses of 4 X 200 mg for 8 days and in a group of untreated healthy subjects. The investigations were made before the treatment on the last day of cimetidine administration, and one week after drug withdrawal. The bactericidal activity of neutrophils was found to be higher in duodenal ulcer patients than in the healthy controls. Cimetidine does not have a significant effect on the phagocytic activity of neutrophils and it has a moderately inhibitory effect (p less than 0.05) on the bactericidal activity relative to the ingested intracellular bacteria. This shows that cimetidine may modify some of the neutrophil functions in duodenal ulcer patients.     

Inhibition of gastric acid secretion by cimetidine in patients with duodenal ulcer.

Cimetidine, a non-thiourea-containing H2-receptor antagonist, was studied in seven patients with duodenal ulcer. Oral doses of 100, 200, and 300 mg were tested. Each dose significantly inhibited basal and meal-stimulated secretion. After 300 mg, basal acid secretion was essentially zero for at least five hours. The meal-stimulated three-hour acid output after the 300-mg dose was reduced by 67%. Cimetidine, 300 mg, decreased meal-stimulated acid secretion significantly more than an optimal effective dose of propantheline bromide (P less than 0.05). Inhibition of meal-stimualted gastric acid secretion showed a significant relation to peak blood cimetidine concentration (r is equal to 0.76, P less than 0.01). Cimetidine did not affect meal-stimulated gastrin release. No toxicity was observed after serial doses given during these tests. Cimetidine may be useful in treatment of acid-peptic diseases provided no important toxicity appears on chronic testing.     

Role of histaminergic H1 and H2 receptors in prolactin release in humans

Histamine is considered as a neurotransmitter, since it is present in hypothalamus and pituitary gland. It has been reported to stimulate prolactin (PRL) release in rats and humans; it seems to be involved in the control of LH release in rats. But cimetidine, an H2 antagonist also induces PRL release in humans. To investigate the relationship between the PRL secretion and possible histaminergic pathways, the response of PRL and LH was studied for 180 minutes in 10 normal subjects (5 men, 5 women) after H1 antagonist (diphenhydramine 50 mg iv), H2 antagonist (cimetidine 300 mg iv) and placebo. Diphenhydramine and placebo injection resulted in a decrease of PRL from 0800 until 11.00 hours, suggesting a spontaneous diurnal variation. Cimetidine induced a short but significant rise of PRL before a similar diurnal secretory pattern. LH levels were unaffected by H1 and H2 antagonists. These data suggest that PRL and LH secretion in humans is unresponsive to H1 histaminergic pathways. The specific action of cimetidine remains to be defined.     

Hypothalamic-pituitary-gonadal dysfunction in men using cimetidine.

We studied the effect of cimetidine therapy (1200 mg per day by mouth for nine weeks) on the hypothalamic-pituitary-gonadal axis of seven men. There was a 43 per cent mean reduction in sperm count after therapy. The luteinizing hormone response to luteinizing hormone releasing factor was also reduced, and a statistically significnat rise in plasma testosterone occurred, although it was less than that before therapy. Gonadotropin responses to provocative clomiphene stimulation were inadequate when compared with those of controls. Cimetidine did not affect the responses of thyroid-stimulating hormone, prolactin, growth hormone and thyroxine to thyrotropin releasing factor. Caution is advisable in administration of cimetidine for prolonged periods to young men.     

Therapeutic effect of cimetidine on acetaminophen-induced nephrotoxicity in rabbits

Acetaminophen is an analgesic and antipyretic drug that can cause nephrotoxicity in humans and experimental animals. Cimetidine is an H₂ blocker used for suppression of gastric acid secretion. One of its side effects is blockade of the cytochrome P-450 enzyme system which results in an increased half-life of some drugs. In this study, 120 female rabbits were randomized into 12 groups (three control and nine test groups). The LD₅₀ of acetaminophen was calculated to be 3.24 g/kg, and a suspension at this concentration was administered orally to induce renal necrosis. Three treatment groups received a single dose of cimetidine (40 mg/kg) administered intravenously at 0, 2, or 4 h after administration of acetaminophen depending upon treatment group. The six remaining treatment groups received cimetidine in two equal doses of 20 mg/kg administered at 0 and 12 h, 0 and 24 h, 2 and 12 h, 2 and 24 h, 4 and 12 h, or 4 and 24 h after the administration of acetaminophen. Blood samples were collected at 0, 12, 24, and 36 h after the induction of acetaminophen toxicity. Blood urea nitrogen and creatinine levels were measured in all groups and were significantly raised in the acetaminophen control group and some treatment groups (p < 0.05). The results indicate that the most effective treatment with cimetidine was obtained with a single dose of cimetidine administered 2 h after acetaminophen intake.     

Effect of an H2-receptor blocking agent on diarrhoeas after extensive small bowel resection in Crohn's disease

The effect of an H2-receptor blocking agent, cimetidine, on faecal losses of fluid, electrolytes and fat was examined in 10 patients with Crohn's disease, who had diarrhoeas after extensive small bowel resection. A randomized, double-blind and cross-over design was applied, and patients were hospitalized and on a defined diet during the study. Cimetidine, 4 x 400 mg, significantly reduced diarrhoeal volumes by an average of 22% (p less than 0.05) and faecal sodium by 27% (p less than 0.05). Patients with severe diarrhoeas responded better to treatment. No side-effects were recorded. The reported data suggest that cimetidine may be useful in symptomatic treatment of patients with severe diarrhoeas after extensive ileal resection. Due to deficient drug absorption, higher doses may be needed for optimal effect.     

Immunomodulatory properties of cimetidine in ARC patients

The immunomodulatory potency of cimetidine, a histamine H2 receptor antagonist, was investigated in 33 AIDS-related complex (ARC) patients performing detailed immunological and clinical evaluations. Cimetidine was administered orally in daily doses of 1200 mg for a period of 5 months with an interruption of therapy after the first 3 months for an interval of 3 weeks. Significant (P less than 0.05) elevations of immunoglobulins (IgG, IgA), complement C4, B-lymphocytes, and OKT4+ (helper/inducer) cells were found after cimetidine intake. The in vitro lymphocyte proliferative response to plant mitogens was significantly increased, and the in vivo cell-mediated hypersensitivity reaction assessed by intradermal application of seven recall antigens improved significantly. These effects were both reversible with the discontinuation of cimetidine and reproducible with repeated administration of the drug. Clinical data such as performance status, body weight, and fever were influenced favorably (P less than 0.05) by cimetidine. The frequency of diarrhea and the lymph node size were also diminished significantly. The data suggest that cimetidine may at least partially restore immunofunctions in AIDS-related complex.     

Inhibition of suppressor cell function by cimetidine in a murine model

Immunomodulatory effects of cimetidine, an H2 histamine receptor antagonist, have been reported in humans and animals. To define these effects more clearly, the action of cimetidine on suppressor cell function was studied utilizing a murine model of contact hypersensitivity. Intravenous inoculation of BALB/c mice with DNP-coupled syngeneic spleen cells induced the production of DNP-specific suppressor cells which could easily be demonstrated by a reduction in ear swelling after contact sensitization with 1-fluoro-2,4-dinitrobenzene (DNFB) following transfer of spleen and lymph node cells to naive syngeneic recipients. Cimetidine treatment of animals in which suppressor cells were induced resulted in an inability of these mice to transfer cellular suppression as measured by development of a normal immunologic response in the recipient mice. The effect of cimetidine was both dose and time related. While all groups receiving cimetidine showed some loss of suppressor cell function, the maximum effect (up to 100% inhibition) was seen when 50 mg/kg of cimetidine was administered intraperitoneally 2 days before or on the day of suppressor cell induction. Some restoration also occurred when cimetidine was given after the day of induction. It has been shown that suppressor cells possess histamine receptors which may be involved in suppressor cell activation. The results indicate that cimetidine may inhibit the functioning of these receptors.     

Therapeutic effect of cimetidine on acetaminophen-induced nephrotoxicity in rats

Acetaminophen as an analgesic and antipyretic drug can induce renal toxicity in high doses. Cimetidine as an H₂-blocker can inhibit the cytochrome P450 enzymes and reduce the toxic effect of acetaminophen on renal tissue. Eighty rats in eight groups comprising normal control group, acetaminophen control group, cimetidine control group, and five different treatment groups (cimetidine was administrated at 0, 1, 2, 4, and 8 h after acetaminophen administration) were used. Acetaminophen was administered at a toxic of dose 3 g/kg orally, and cimetidine (12.5 mg/kg) was administrated by intraperitoneal route at different times after induction of toxicity. Creatinine and urea were measured, and pathologic lesions were determined. In treatment groups 3 and 6, the urea and creatinine concentration showed no significant difference from group 1. In other treatment groups, the urea and creatinine concentrations were increased significantly (p < 0.05). Histopathologic changes in group 6 were mild in comparison to other groups. We concluded that administration of cimetidine at least 2 h after acetaminophen toxicity can reduce renal lesions.     

Cimetidine abrogates suppressor T cell function in vitro

Cimetidine increased the [3H] thymidine incorporation of normal human mononuclear cells in culture both when unstimulated or when under the stimulus of phytohemagglutinin or pokeweed mitogen (PWM). It also increased their supernatant immunoglobulin production under PWM stimulus. These effects were higher when the cells were preincubated with cimetidine than when it was added simultaneously. To determine if this effect of cimetidine reflects an abrogation of suppression we studied concanavalin-A-induced suppressor function of normal mononuclear cells using both [3H] thymidine incorporation and immunoglobulin synthesis as indicator systems and found that preincubation with cimetidine caused significant decrease in suppressor cell function in both systems.     

Different effects of cimetidine and ranitidine on gastric emptying in rats and man

Cimetidine and ranitidine were tested for their effect on gastric emptying in the rat. At low doses, cimetidine was inactive, whereas it significantly delayed emptying rate when administered at higher doses. Ranitidine always accelerated gastric emptying. At variance with rats, ranitidine delayed human gastric emptying whereas cimetidine was completely inactive. All these data are consistent with the idea that these effects of H₂-antagonists are independent of H₂-receptor blockade.     

Leukopenia with Cimetidine

A case of leukopenia associated with cimetidine therapy is reported. The patient had sarcoid cirrhosis with portal hypertension. Cimetidine therapy was instituted for upper gastrointestinal bleeding due to gastritis, resulted in leukopenia, and was reversed on discontinuation of therapy.