Comparison of Effects of Metformin, Phenformin, and Inhibitors of Mitochondrial Complex I on Mitochondrial Permeability Transition and Ischemic Brain Injury

Damage to cerebral mitochondria, particularly opening of mitochondrial permeability transition pore (MPTP), is a key mechanism of ischemic brain injury, therefore, modulation of MPTP may be a potential target for a neuroprotective strategy in ischemic brain pathologies. The aim of this study was to investigate whether biguanides-metformin and phenformin as well as other inhibitors of Complex I of the mitochondrial electron transfer system may protect against ischemia-induced cell death in brain slice cultures by suppressing MPTP, and whether the effects of these inhibitors depend on the age of animals. Experiments were performed on brain slice cultures prepared from 5-7-day (premature) and 2-3-month old (adult) rat brains. In premature brain slice cultures, simulated ischemia (hypoxia plus deoxyglucose) induced necrosis whereas in adult rat brain slice cultures necrosis was induced by hypoxia alone and was suppressed by deoxyglucose. Phenformin prevented necrosis induced by simulated ischemia in premature and hypoxia-induced-in adult brain slices, whereas metformin was protective in adult brain slices cultures. In premature brain slices, necrosis was also prevented by Complex I inhibitors rotenone and amobarbital and by MPTP inhibitor cyclosporine A. The latter two inhibitors were protective in adult brain slices as well. Short-term exposure of cultured neurons to phenformin, metformin and rotenone prevented ionomycin-induced MPTP opening in intact cells. The data suggest that, depending on the age, phenformin and metformin may protect the brain against ischemic damage possibly by suppressing MPTP via inhibition of mitochondrial Complex I.

Phenformin Enhances the Efficacy of ERK Inhibition in NF1-Mutant Melanoma

Inactivation of the tumor suppressor neurofibromin 1 (NF1) presents a newly characterized melanoma subtype, for which currently no targeted therapies are clinically available. Preclinical studies suggest that extracellular signal-regulated kinase (ERK) inhibitors are likely to provide benefit, albeit with limited efficacy as a single agent; therefore, there is a need for rationally designed combination therapies. Here, we evaluate the combination of the ERK inhibitor SCH772984 and the biguanide phenformin. A combination of both compounds showed potent synergy in cell viability assays and cooperatively induced apoptosis. Treatment with both drugs was required to fully suppress mechanistic target of rapamycin signaling, a known effector of NF1 loss. Mechanistically, SCH772984 increased the oxygen consumption rate, indicating that these cells relied more on oxidative phosphorylation upon treatment. Consistently, SCH772984 increased expression of the mitochondrial transcriptional coactivator peroxisome proliferator-activated receptor gamma, coactivator 1-α. In contrast, cotreatment with phenformin, an inhibitor of complex I of the respiratory chain, decreased the oxygen consumption rate. SCH772984 also promoted the expansion of the H3K4 demethylase KDM5B (also known as JARID1B)-positive subpopulation of melanoma cells, which are slow-cycling and treatment-resistant. Importantly, phenformin suppressed this KDM5B-positive population, which reduced the emergence of SCH772984-resistant clones in long-term cultures. Our results warrant the clinical investigation of this combination therapy in patients with NF1 mutant melanoma.

[Effect of phenformin hydrochloride on pharmacokinetics of puerarin in rats]

OBJECTIVE

To study the effect of phenformin hydrochloride that may be illegally added in traditional Chinese medicine preparations on the pharmacokinetics of puerarin in rats.

METHOD

Rats were randomly divided into the single pueraria group and the phenformin hydrochloride combined with pueraria group. After oral administration in the two groups, their bloods were sampled at different time points to determine the drug concentration of puerarin in rat blood and calculate pharmacokinetic parameters.

RESULT

After oral administration with pueraria extracts and phenformin hydrochloride combined with pueraria extracts, the two groups showed main pharmacokinetic parameters as follows: Cmax were (2.39 +/- 1.01), (1.03 +/- 0.35) mg x L(-1), respectively; Tmax were (0.50 +/- 0.09), (1.5 +/- 0.5) h, respectively; Ke were (0.153 +/- 0.028), (0.172 +/- 0.042) h(-1), respectively; t(1/2) were (4.65 +/- 0.86), (4.20 +/- 0.81) h, respectively; AUC(0-t), were (5.73 +/- 2.60), (5.45 +/- 1.81) mg x h x L(-1), respectively; AUC(0-infinity) were (6.72 +/- 2.89), (6.26 +/- 1.88) mg x h x L(-1), respectively. Compared with the single puerarin group, the Cmax was significantly decreased (P < 0.05) and the Tmax was markedly longer (P < 0.01) than the hydrochloride combined with pueraria group.

CONCLUSION

Phenformin hydrochloride can slow down the absorption process of puerarin and change the pharmacokinetic process of puerarin to some extent.

Addition of 2-deoxyglucose enhances growth inhibition but reverses acidification in colon cancer cells treated with phenformin

A report that effects of butyrate on some cells may be mediated by activation of AMP-activated protein kinase (AMPK) prompted this study which examines if other AMPK activators can induce differentiation and inhibit proliferation of colon cancer cells in a manner similar to butyrate. Using induction of alkaline phosphatase as a marker, it was observed that compound C, an AMPK inhibitor, is able to reduce the differentiating effect of butyrate on SW1116 and Caco-2 colon cancer cells. Metformin was observed to be less effective than butyrate in the induction of alkaline phosphatase but was more effective as a growth inhibitor. Phenformin was found to be a more potent growth inhibitor than metformin and both compounds cause acidification of the medium when incubated with colon cancer cells. Combined incubation of 2-deoxyglucose with either of the biguanides prevented the acidification of the medium but enhanced the growth inhibitory effects.

Metformin and phenformin activate AMP-activated protein kinase in the heart by increasing cytosolic AMP concentration

AMP-activated protein kinase (AMPK) acts as a cellular energy sensor: it responds to an increase in AMP concentration ([AMP]) or the AMP-to-ATP ratio (AMP/ATP). Metformin and phenformin, which are biguanides, have been reported to increase AMPK activity without increasing AMP/ATP. This study tests the hypothesis that these biguanides increase AMPK activity in the heart by increasing cytosolic [AMP]. Groups of isolated rat hearts (n = 5-7 each) were perfused with Krebs-Henseleit buffer with or without 0.2 mM phenformin or 10 mM metformin, and (31)P-NMR-measured phosphocreatine, ATP, and intracellular pH were used to calculate cytosolic [AMP]. At various times, hearts were freeze-clamped and assayed for AMPK activity, phosphorylation of Thr(172) on AMPK-alpha, and phosphorylation of Ser(79) on acetyl-CoA carboxylase, an AMPK target. In hearts treated with phenformin for 18 min and then perfused for 20 min with Krebs-Henseleit buffer, [AMP] began to increase at 26 min and AMPK activity was elevated at 36 min. In hearts treated with metformin, [AMP] was increased at 50 min and AMPK activity, phosphorylated AMPK, and phosphorylated acetyl-CoA carboxylase were elevated at 61 min. In metformin-treated hearts, HPLC-measured total AMP content and total AMP/ATP did not increase. In summary, phenformin and metformin increase AMPK activity and phosphorylation in the isolated heart. The increase in AMPK activity was always preceded by and correlated with increased cytosolic [AMP]. Total AMP content and total AMP/ATP did not change. Cytosolic [AMP] reported metabolically active AMP, which triggered increased AMPK activity, but measures of total AMP did not.

Regulation of the atherogenic properties of vascular smooth muscle proteoglycans by oral anti-hyperglycemic agents

The present study aimed to investigate the actions of several classes of oral hypoglycemic agents [e.g., sulfonylureas (SUs), biguanides (BGs) and thiazolidinediones (TZDs)] in an in vitro model of lipid binding based on the "response to retention" hypothesis of atherogenesis. The incorporation of [(35)S]-SO(4) into proteoglycans synthesized by human vascular smooth muscle cells (VSMCs) was assessed by cetylpyridinium chloride (CPC) precipitation method, proteoglycan electrophoretic mobility was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and binding to low-density lipoprotein (LDL) was assessed by gel mobility shift assay (GMSA). The SUs evaluated showed no effect on [(35)S]-SO(4) incorporation into proteoglycans. Only one BG, phenformin, caused a concentration-related inhibition of proteoglycan synthesis under basal conditions and in the presence of transforming growth factor-beta1 (TGF-beta1), caused by an inhibition of proteoglycan core protein synthesis secondary to a reduction in total protein synthesis. However, neither metformin nor phenformin (30-300 micromol/l) had any effect on the electrophoretic mobility of proteoglycans. The TZDs--troglitazone (TRO), rosiglitazone (ROS), and pioglitazone (PIO) (10, 30, and 30 micromol/l, respectively)--inhibited proteoglycan biosynthesis and stimulated total proteoglycan core protein synthesis, while TRO alone inhibited overall protein synthesis. All three TZDs moderately reduced the electrophoretic mobility of synthesized proteoglycans assessed by SDS-PAGE, reduced the sizes of cleaved glycosaminoglycan (GAG) chains assessed by size exclusion chromatography, and significantly reduced binding to LDL. The data indicate that TZDs show anti-atherogenic actions through the modification of proteoglycan structure, leading to a possible reduction in lipid retention in the vessel wall.

Phenformin and 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) activation of AMP-activated protein kinase inhibits transepithelial Na+ transport across H441 lung cells

Active re-absorption of Na+ across the alveolar epithelium is essential to maintain lung fluid balance. Na+ entry at the luminal membrane is predominantly via the amiloride-sensitive Na+ channel (ENaC) down its electrochemical gradient. This gradient is generated and maintained by basolateral Na+ extrusion via Na+,K+-ATPase an energy-dependent process. Several kinases and factors that activate them are known to regulate these processes; however, the role of AMP-activated protein kinase (AMPK) in the lung is unknown. AMPK is an ultra-sensitive cellular energy sensor that monitors energy consumption and down-regulates ATP-consuming processes when activated. The biguanide phenformin has been shown to independently decrease ion transport processes, influence cellular metabolism and activate AMPK. The AMP mimetic drug 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) also activates AMPK in intact cells. Western blotting revealed that both the alpha1 and alpha2 catalytic subunits of AMPK are present in Na+ transporting H441 human lung epithelial cells. Phenformin and AICAR increased AMPK activity in H441 cells in a dose-dependent fashion, stimulating the kinase maximally at 5-10 mm (P = 0.001, n = 3) and 2 mm (P < 0.005, n = 3), respectively. Both agents significantly decreased basal ion transport (measured as short circuit current) across H441 monolayers by approximately 50% compared with that of controls (P < 0.05, n = 4). Neither treatment altered the resistance of the monolayers. Phenformin and AICAR significantly reduced amiloride-sensitive transepithelial Na+ transport compared with controls (P < 0.05, n = 4). This was a result of both decreased Na+,K+-ATPase activity and amiloride-sensitive apical Na+ conductance. Transepithelial Na+ transport decreased with increasing concentrations of phenformin (0.1-10 mm) and showed a significant correlation with AMPK activity. Taken together, these results show that phenformin and AICAR suppress amiloride-sensitive Na+ transport across H441 cells via a pathway that includes activation of AMPK and inhibition of both apical Na+ entry through ENaC and basolateral Na+ extrusion via the Na+,K+-ATPase. These are the first studies to provide a cellular signalling mechanism for the action of phenformin on ion transport processes, and also the first studies showing AMPK as a regulator of Na+ absorption in the lung.

Sustaining pattern of phenformin hydrochloride using various polymers and waxes

The present study was carried out to formulate matrix tablets of phenformin hydrochloride. Granules of phenformin HCl were prepared by using ethyl cellulose, eudragit RS 100, gum acacia, carnauba wax, stearyl alcohol, glyceryl monostearate and triethanol amine. Thus the granules were compressed and fourteen tablets formulations were prepared. All the physical parameters of granules and matrix tablets were studied including compatibility study. One commercial timed disintegration capsule was also included for study and comparison. The results of in vitro studies showed that sustained release matrix tablet might be prepared using carnauba wax, stearyl alcohol, triethanol amine and magnesium stearate.

Levels of lactic acid, normal level & its relation to food, glucose, cholesterol, raised blood urea and phenformin therapy

1. The level of lactic acid was found to be 25 mg percent in 95 percent of 186 normal Indians. There was no difference due to sex and age. 2. Level of lactic acid was estimated in blood of normal persons and diabetics Type II patients to observe the effects of food and glucose. There was no change except the level of lactic acid was in higher but in normal range. 3. Hyperglycemia of over 300 mg raised the blood lactic acid in 25 percent of patients. 4. Lactic acid was not affected by hypercholesteremia but was raised in 60 percent of cases with raised blood urea. 5. Lactic acid was found to remain within normal limits in 48 type II diabetics treated with phenformin dose varying from 50 mg to 225 mg per day. The duration of treatment varied from one year to seven years.

Vanadyl-biguanide complexes as potential synergistic insulin mimics

Vanadium has well-documented blood-glucose-lowering properties both in vitro and in vivo. The design of new oxovanadium(IV) coordination compounds, intended for use as insulin-enhancing agents in the treatment of diabetes mellitus, can potentially benefit from a synergistic approach, in which the whole complex has more than an additive effect from its component parts. Biguanides, most importantly metformin, are oral hypoglycemic agents used today to treat type 2 diabetes mellitus. In this study, biguanide, metformin, and phenformin, all biguanides, were coordinated to oxovanadium(IV) to form potential insulin-enhancing compounds. Highly colored, air-stable, bis(biguanidato)oxovanadium(IV), [VO(big)2], bis(N'N'-dimethylbiguanidato)oxovanadium(IV), [VO(metf)2], and bis(beta-phenethyl-biguanidato)oxovanadium(IV), [VO(phenf)2], were prepared. Solvation with dimethylsulfoxide occurred with VO(metf)2 to form a six-coordinate complex. Precursor ligands and oxovanadium(IV) coordination complexes were characterized by infrared spectroscopy, mass spectrometry, elemental analyses, magnetic susceptibility, and, where appropriate, 1H NMR spectroscopy. Biological testing with VO(metf)2, a representative compound, for insulin-enhancing potential included acute (72 h) administration, both by intraperitoneal (i.p.) injection and by oral gavage (p.o.) in streptozotocin (STZ)-diabetic rats. VO(metf)2 administration resulted in significant blood-glucose lowering at doses of 0.12 mmol kg-1 i.p. and 0.60 mmol kg-1 p.o. (previously established as ED50 doses for organically chelated oxovanadium(IV) complexes); however, no positive associative effects due to the presence of biguanide in the complex were apparent.

[Short-term intensive insulin therapy as a method of overcoming secondary failure of sulfonylureas in patients with type 2 diabetes (non-insulin-dependent)]

The study group comprised 56 patients (25 males and 31 females) with type 2 diabetes in whom the secondary failure to sulphonylurea derivates (SU) had developed. All patients were submitted for 14 days to therapy with 5 injections of insulin per day in total dose of insulin permitting to decrease the mean daily glycaemia below 8.8 mmol/l (160 mg/dl). After the termination of the intensive insulin therapy (IIT) the patients with insulin requirement below 44 U daily were alternatively qualified to treatment with SU (glybenclamide) alone or with this SU plus biguanide derivate (BG: phenformin), and those who needed more than 44 U daily continued conventional therapy with insulin alone or with insulin plus SU (glybenclamide). There was a marked reduction of fasting and postprandial blood glucose during the IIT and over the subsequent 15 months of the follow-up. The mean glycaemia which initially was in fasting state 12.5 +/- 2.4 mmol/l (225 +/- 43 mg/dl) and 2 hours after breakfast 18.1 +/- 2.8 mmol/l (325 +/- 50 mg/dl) decreased significantly and was in four groups between 8.0 +/- 0.3 mmol/l (144 +/- 5 mg/dl) and 10.8 +/- 0.5 mmol/l (194 +/- 9 mg/dl) in fasting state and between 10.5 +/- 0.3 (189 +/- 5 mg/dl) and 11.2 +/- 0.4 mmol/l (201 +/- 7 mg/dl) after breakfast. The least hypoglycaemic effect was found in patients who after IIT were treated exclusively with insulin (mean daily dose 53 +/- 2 IU) while the decrease of glycaemia was most evident in patients treated with SU given as a single drug or in combination with BG or with insulin (mean daily dose 19 +/- 1 IU). In all studied patients basal and stimulated (1 mg glucagon i.v.) C-peptide secretion markedly decreased during IIT, and greatly increased after its termination, and this increase persisted over following 15 months of observation, correlating with the initial values.

CONCLUSIONS

The short-term IIT in patients with NIDDM and secondary failure to SU is effective in reducing hyperglycaemia, and in most of them makes possible to continue the oral antidiabetic treatment with SU. The secretion of endogenous insulin seems to have only limited influence on the metabolic control of the patients treated with four different pharmacological regiments after IIT.

Therapeutic effect of glibenclamide in a fixed combination with metformin or phenformin in NIDDM patients

The combination of a sulfonylurea with a biguanide improves the pancreatic beta-cell insulin secretion and the insulin utilization in peripheral tissues in NIDDM. This open, crossover, randomised and prospective study was designed to compare the effects of the fixed combination glibenclamide-metformin (GL-METF)-2.5 and 400 mg respectively, with the fixed combination glibenclamide-phenformin (GL-PHEN)-2.5 and 25 mg respectively, on NIDDM diabetes control. Thirty NIDDM patients, in ideal metabolic control, who were being treated with GL-PHEN were divided in two groups. One group received GL-PHEN for 12 weeks followed by 12 weeks treatment with GL-METF and the reverse treatment was given to the second group. A statistically significant decrease of post-prandial blood glucose (p = 0.034) and glycosylated haemo-globin (p < 0.02) values was observed under GL-METF treatment compared to those with GL-PHEN. The values of lactic acid were within normal limits during both treatments. The insulin secretion after breakfast was similar with both drug compounds. The BMI of the patients remained the same during a follow-up study of 24 weeks. Lipid metabolism did not change significantly during the trial and the safety parameters (renal and liver function, full blood count) remained unchanged. In conclusion, the administration of GL-METF leads to better diabetes control in NIDDM patients compared to that of GL-PHEN.

Effect of bed time intermediate acting insulin in NIDDM subjects refractory to a combination of sulphonylureas and biguanides

The effect of a single dose of intermediate acting (Lente) insulin given subcutaneously at 9.00 P.M. in 22 NIDDM subjects refractory to a combination of Sulphonylureas and Biguanides was analysed. Euglycemia was achieved and maintained during the study period of three months with a mean insulin requirement of 14.22 +/- 5.98 units/day. Plasma FFA, Total cholesterol, triglyceride and VLDL-cholesterol also showed significant reduction. The level of FFA modulates hepatic glucose production, which in turn correlates positively with the fasting blood glucose. The therapeutic modality of bed time Lente Insulin based on physiological principles is an effective way of achieving glycemic control in NIDDM subjects who have become non-responsive to oral hypoglycemic agents.

Teicoplanin does not modify the hypoglycemic effects of phenformin or glibenclamide, nor the anticoagulant action of warfarin. Experimental study

Eventual pharmacological interactions induced by teicoplanin administration associated with oral hypoglycemic (phenformin and glibenclamide) and oral anticoagulant (warfarin) drugs have been experimentally evaluated. The administration of teicoplanin (3-15 mg/kg/die by endoperitoneal route) to the rat for 4 days did not significantly (P greater than 0.05) modify glycemia, prothrombin and partial thromboplastin times, the hypoglycemic effect of phenformin (2.5 mg/kg/die/4 days) or glibenclamide (0.5 mg/kg/die/4 days) nor the anticoagulant effect of warfarin (0.5 mg/kg/die/4 days). In conclusion, our results document that teicoplanin does not interfere with the activity of phenformin, glibenclamide or sodium warfarin.

[Efficacy of sulfonylurea and sulfonylurea-benfluorex therapy in patients with type 2 diabetes treated with commercial sulfonylurea-biguanide combinations]

This study tests the possibility to avoid the use of phenformin in 40 type 2 (non insulin dependent) diabetic patients treated with the commercial sulphonylurea-phenformin combinations. In diabetic patients treated with sulphonylureas and phenformin at low dosage (glibenclamide 5 mg and phenformin 50 mg) it was possible to maintain good glycometabolic control using only the sulphonylurea gliclazide (160 mg/die). The diabetic patients on treatment with sulphonylureas and phenformin at higher dosage (glibenclamide 7.5 mg and phenformin 75 mg) may further improve their metabolic control when transferred to a gliclazide-benfluorex combination 160 mg and 300 mg/die, respectively. These results suggest the possibility of withdrawing or replacing phenformin in the therapy of type 2 diabetic patients without modifying their glycometabolic control.

Carbohydrate biguanides as potential hypoglycemic agents

A series of monosaccharides containing a biguanide functionality was prepared and evaluated for hypoglycemic activity. Among the analogues prepared were those involving D-glucose substituted on the 6- or 1-position (19 and 24), D-galactose substituted on the 6-position (7), and D-arabinose (31). The target compounds were evaluated in a modified rat glucose-tolerance test (oral glucose load/oral drug, 100 mg/kg). Compounds 8 [6-biguanidino-1,2:3,5-bis-O-(1-methylethylidene)-6-deoxy-al pha-D- glucofuranose] and 23 [methyl 6-biguanidino-6-deoxy-2,3,4-O-tribenzyl-alpha-D-glucopyra nos ide] were the most active, exhibiting nearly equivalent hypoglycemic activity to that of phenformin (1) and metformin (2), as measured by the inhibition of the rise of blood glucose. Compound 31 was somewhat less active with 26% inhibition, as compared to 64% inhibition with 1 and 41% inhibition with 2.

[Evaluation of the late ineffectiveness of sulfonylurea derivatives in patients with diabetes mellitus hospitalized at the Gastroenterology and Metabolic Disease Clinic, Medical Academy, in Warsaw 1976-1987]

The authors made a retrospective analysis of late ineffectiveness of sulphonylurea derivatives and its correlation with the age of diabetes onset, duration of the disease, sex, body mass, smoking cigarettes, diabetes history in the family, coexistence with some diabetic complications as retinopathy, ischemic heart disease, arterial hypertension and vascular diseases in lower limbs. The study was carried out in a group of 220 patients with diabetes type 2 lasting from 1 up to 25 years, aged 30-77 undergoing therapy in the Department of Gastroenterology and Metabolic Diseases in the years 1976-1987 in whom a late ineffectiveness appeared to sulphonylurea derivatives. The average time of effective therapy by means of sulphonylurea derivatives in the group examined was 8.7 +/- 4.9 years (9.2 +/- 5.2 in men and 8.3 +/- 4.6 in women). The time of effective therapy by means of the above drugs was inversely proportional to the age of patients when diabetes type 2 appeared. The time of effective therapy by means of sulphonylurea derivatives in obese men was significantly longer than in obese women. No correlation was found between the appearance of late ineffectiveness of sulphonylurea derivatives and diabetes history in the family, smoking ischemic heart disease, arterial hypertension, retinopathy and vascular diseases of lower limbs.

[Effect of fenformin and miscleron on the delayed hypersensitivity reaction in breast cancer patients]

Some preliminary results of using phenformin and miscleron in 17 breast cancer patients, previously radically operated upon, have been assessed as being characterized by metabolic disturbances associated with the reduced cell immunity level. The treatment of patients during 15--7 months was shown to result both in the correction of endocrine-metabolic disorders and stimulation of delayed hypersensitivity response, determined by skin tests with dinitro-chlorbenzene, tuberculin and Candida. The necessity to liquidate metabolic metabolic immunodepression with the aim of prophylaxis and treatment of the tuumor process is discussed. Some other routes of metabolic immunotherapy in addition to using phenformin and miscleron are considered. It seems rational to study the effect of a continuous administration of such kind of drugs on the results of treatment of oncological patients.

Metabolism of phenformin in the rat and guinea-pig

1. Following administration of [2'-14C]phenformin to rat and guinea pig, the guinea-pig showed a slower rate of excretion of radioactivity than the rat, together with a slower rate of metabolism, which may partly explain the increased pharmacological response of the guinea-pig to the drug. 2. The rat eliminated 26% of an intraduodenal dose of [2'-14C]phenformin (20 mg/kg) in the bile in 6 h compared to 6% in the guinea-pig. 3. The rat excreted large amounts of 4-hydroxyphenformin (free and conjugated with glucuronic acid) and also some unchanged phenformin, but the extent of metabolism varied with dose and route of administration. 4. The guinea-pig excreted no 4-hydroxyphenformin after an oral dose (25 mg/kg) and only a small amount after i.p. administration (12.5 mg/kg). After oral administration, guinea-pig urine contained an unidentified metabolite, and its glucuronide, which may be a product of aliphatic C- or N-hydroxylation and which accounted for 47% of the 24 h urinary radioactivity (17% of the dose). Guinea-pig faeces contained an unidentified metabolite which had similar chromatographic properties to the novel urinary metabolite.

Potentiation of antitumor effect of cyclophosphamide and hydrazine sulfate by treatment with the antidiabetic agent, 1-phenylethylbiguanide (phenformin)

It was shown that 1-phenylethylbiguanide (phenformin) administered orally to mice at a dose of 2 mg/day potentiated the antitumor effect of cyclophosphamide on transplantable squamous cell cervical carcinoma, hepatoma-22a and Lewis lung tumor, but did not alter the effect of cyclophosphamide on sarcoma-180 and L-1210. Oral administration of phenformin (5 mg/day) to rats with transplanted Walker 256 carcinoma enhanced the antitumor effect of hydrazine sulfate.

Acute muscle necrosis after chronic overdosage of phenformin and fenfluramine

A case of acute muscle necrosis with probable myoglobinuria is presented. The patient had been taking excessive doses of phenformin and fenfluramine, and a toxic etiology is suggested. Muscle necrosis is tentatively attributed either to the combined effect of these drugs on some underlying biochemical abnormality of muscle or to a defect of oxygen utilization secondary to myoglobin alterations.

Determination of oral anti-diabetic agents in human body fluids using high-performance liquid chromatography

Two widely prescribed anti-diabetic agents for which no simple assay method was previously available can now be determined by high-performance liquid chromatography using a UV detection system. The two drugs investigated were tolbutamide (a sulphonylurea) and phenformin (a biguanide). Tolbutamide can be assayed directly, after a single extraction step, on a reversed-phase system, illustrating the simplicity of the technique for carrying out analyses on underivatised drug compared with gas chromatography. Phenformin was not so easily chromatographhed using straightforward partition systems; however, by the choice of a suitable ion-pair agent it was possible to chromatograph the underivatised drug in a relatively simple reversed-phase system.

Treatment of borderline diabetes: controlled trial using carbohydrate restriction and phenformin

A five-year therapeutic trial of carbohydrate restriction with or without phenformin (50 mg/day) was performed in men with borderline diabetes. The aim of treatment was to diminish the enhanced risk of cardiovascular disease and deterioration of glucose tolerance. Cardiovascular morbidity and mortality were not significantly affected by any form of treatment, alone or in combination. The predominant risk factor for cardiovascular morbidity and mortality and for overall mortality was the initial blood pressure level. The baseline plasma cholesterol concentration significantly predicted the onset of intermittent claudication. One implication of the results is that hypotensive treatment, supplemented when necessary with hypolipidaemic treatment, may be more effective in preventing the progression of arterial disease in people with mild to moderate glucose intolerance than conventional antidiabetic therapy.

[Treatment of primary hyperlipoproteinemia type IIb and IV. Comparison of the lipid lowering effect of phenformin, clofibrate, and a combination of both (author's transl)]

22 outpatients with primary hyperlipoproteinemia type IIb and IV were treated in periods of eight weeks as follows: placebo; 0,15 g phenformin/day; 0,15 g phenformin + 1,5 g clofibrate/day; 1,5 g clofibrate/day; placebo. Compared to the first placeboperiode the serumtriglycerides were significantly lowered by phenformin (about 26%), by the combined treatment with phenformin + clofibrate (60%) and by clofibrate (51%) after eight weeks of treatment. The serumcholesterol was significantly lowered by phenformin (10%) and by the combined treatment with phenformin and clofibrate (14%), but not significantly by clofibrate (8%). After eight weeks of treatment with phenformin alone or in combination with clofibrate the body weight decreased significantly (1,9% or 1,4%). These changes in body weight were not related to changes in blood lipids. In conclusion, the combined treatment with 0,15 g clofibrate/day was more effective in lowering increased serum lipids than the treatment with phenformin or clofibrate alone.

The effect of chronic oral antidiabetic therapy on insulin and glucagon responses to a meal

Nineteen maturity-onset diabetic patients receiving oral hypoglycemic therapy in a university diabetes clinic completed a study to assess the efficacy of the oral agents and to determine their effects on pancreatic islet hormone secretion. All patients were receiving sulfonylureas, and seven were also receiving phenformin. The subjects were studied as outpatients in the clinic setting on four different occasions with collections of a baseline blood sample before a standard breakfast and a second sampling two hours postprandially, twice while on their prescribed medication and twice after having been withdrawn from the medication. The values obtained during the two studies on the two studies off medications were reproducible for each subject. Analysis of the results by paired differences revealed that mean 24-hour urine glucose values deteriorated significantly (p less than 0.005) after oral antidiabetic therapy was withdrawn; similarly, mean plasma glucose values, both at baseline and two hours postprandially, rose significantly (p less than 0.001) when subjects were off medication. Baseline serum insulin values were not changed, but postprandial levels were significantly higher on oral agents (p less than 0.005). Plasma immunoreactive glucagon was significantly lower both at baseline (p less than 0.02) and postprandially (p less than 0.005) when the subjects were on their antidiabetic medications. During the trial off medication, 16 patients became symptomatic, with three of these developing symptoms severe enough to require hospitalization. It is apparent from this study that oral hypoglycemic medications can play a role in controlling symptoms in maturity-onset diabetic patients and that the beneficial effect of these agents on hyperglycemia may, in part, be explained by their stimulation of endogenous insulin secretion and partial suppression of endogenous glucagon.

Can phenformin-induced lactic acidosis be prevented?

Although patients taking phenformin are more likely to develop lactic acidosis in the presence of renal, cardiovascular, or hepatic disease, criteria for safe use of the drug are not well established. Eight diabetics died of lactic acidosis in Nottingham in 1972-5 and all were taking phenformin in therapeutic doses. Six had attended the diabetic clinic within a month of their terminal illness. Two patients had appreciable renal impairment and should not have been given phenformin. Four had hypertension and minimal evidence of renal disease, while in two no predisposing factor was identified. There are so many contraindications to the use of phenformin that it is doubtful whether patients on the drug can be monitored adequately. We suggest that phenformin should be withdrawn from general use.

Potentiation of hypoglycemic effect of sulfonylureas by halofenate

We investigated the possibility of a drug interaction between the antilipemic agent halofenate and sulfonylureas. Twelve young, healthy men were given 1 g of tolbutamide by mouth before and after 12 days of double-blind treatment with 1 g per day of halofenate, or placebo. There was a significant increase in serum tolbutamide at eight, 10 and 12 hours (P less than 0.01) and a significant (P less than 0.01) decrease in serum glucose at one, four and six hours after halofenate treatment, but not after placebo. In a long-term, double-blind study of halofenate or clofibrate treatment of patients with Type IV hyperlipoproteinemia, diabetic patients receiving a sulfonylurea and halofenate either required a reduction in the dose of the sulfonylurea or demonstrated significantly improved control of hyperglycemia (P less than 0.05) or both. No appreciable decrease in serum glucose levels was noted in diabetic patients receiving sulfonylurea and clofibrate. This interaction between halofenate and sulfonylureas is clinically important, especially in view of the association of hyperlipemia and diabetes.