Recollections from the Kunkel laboratory, 1956-1958

The Kunkel laboratory provided a unique environment for dedicated young scientists to learn the art of clinical investigation.

The pursuit of clinical truth: role of epidemiology/observation studies

The need for evidence-based medicine as a foundation for optimal patient care requires application of the best scientific methods. Various methods used in the search for clinical truth are discussed. The most powerful method to test a clinical hypothesis is the randomized, controlled clinical trial. By contrast, epidemiology/observation studies (EOS) have inherent weaknesses that can lead to erroneous conclusions. Five such examples, two older and three very recent, are discussed to provide historical perspective and demonstrate potential problems with EOS. Each incident has produced widespread consternation or confusion among physicians. Types of bias leading to errors in EOS are discussed, and the need is emphasized for more rigorous evaluation of EOS by investigators, as well as editors, to avoid repetition of past mistakes and to ensure publication of correct medical information.

Advances in pharmacogenetics and pharmacogenomics

Large differences among normal human subjects in the efficacy and safety of many therapeutic agents are caused by genetically controlled polymorphisms of drug-metabolizing enzymes, drug transporters, and drug receptors. Development of pharmacogenomics as a new field has accelerated progress in pharmacogenetics by elucidating at the level of the human genome the inherited basis for those large interindividual variations. Examples discussed in this review illustrate how this approach can be used not only to guide new drug discovery but also to individualize therapy. Adverse drug reactions, often attributable to large differences among subjects in drug response, constitute a leading cause of death in the USA. Such high morbidity and mortality could be reduced by application of the principles of pharmacogenetics and pharmacogenomics, defined broadly as the study of genetically caused variability in drug response.

Studies on pyrazinoylguanidine: a novel antihypertensive, hypoglycemic and lipolytic drug intended for adjunctive use in hypertensive patients with type 2 diabetes mellitus

Herein are described the development and certain properties of a new drug, pyrazinoylguanidine (PZG), intended for use as an adjunct in the treatment of hypertensive patients with type 2 diabetes, formerly called noninsulin dependent diabetes mellitus. PZG is an analog of the potassium sparing diuretic, amiloride. However, in diabetic patients, amiloride exacerbates hyperglycemia and hyperlipidemia, whereas PZG reduces them. In several studies, PZG not only reduced elevated blood pressure in subjects with essential hypertension, but also downregulated the glucose fatty acid cycle in hypertensive patients with type 2 diabetes. PZG was well tolerated in all patients, as well as in normal subjects whose blood pressures and glucose metabolism were unaffected by PZG. However, in normal subjects made hyperglycemic by giving them hydrochlorothiazide, coadministration of PZG returned blood glucose concentrations to normal. Mechanisms for these effects of PZG in human subjects were investigated in both normal Sprague-Dawley rats and rats made diabetic with streptozotocin (STZ). In isolated rat adipocytes stimulated with theophylline, PZG downregulated both lipolysis and cyclic AMP concentrations. PZG, as well as insulin, increased adipose cyclic nucleotide phosphodiesterase activity, whereas theophylline reduced it. In perfused rat liver, PZG decreased gluconeogenesis and cyclic AMP concentrations. Collectively, these studies illustrate how the side effects (toxicity) of certain drugs, such as the tendency of thiazide diuretics to cause hyperglycemia and hyperlipidemia, can be modulated and even reversed by slight changes in the chemical structure of the molecule, specifically by removal of the 3,5-diamino and 6-chloro substituents on the benzene ring of amiloride to produce PZG.

Are the elderly underrepresented in clinical drug trials?

In many industrialized nations, the elderly comprise the fastest growing subpopulation and constitute an increasing proportion of the total population compared to other age groups. The elderly use a disproportionately larger amount of health care resources since they experience a higher incidence of disease-related morbidities, consume more drugs, are subject to more extensive multiple medication regimens, and account for more adverse drug events. In response to the great demand for geriatric pharmacotherapy, the pharmaceutical industry has targeted more drugs to the elderly. However, the elderly are too often excluded from clinical trials on drugs primarily destined for their consumption. Comprehensive analyses to assess participation of elderly subjects in clinical drug trials are needed to design and implement trials that will enhance the safety and efficacy of drugs intended for this pharmacologically sensitive subpopulation.

Metabolism and disposition of 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK) in rhesus monkeys

Metabolism and disposition of the tobacco-specific N-nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent rodent lung carcinogen, were studied in rhesus monkeys. In three males receiving a single i.v. dose of [5-3H]NNK (0.72 mCi; 4.6-9.8 microg/kg), urine was collected for 10 days. Within the first 24 h, 86.0 +/- 0.7% of the dose was excreted. NNK-derived radioactivity was still detectable in urine 10 days after dosing (total excretion, 92.7 +/- 0.7%). Decay of urinary radioactivity was biexponential with half-lives of 1.7 and 42 h. Metabolite patterns in urine from the first 6 h closely resembled those reported previously for patas monkeys; end products of metabolic NNK activation represented more than 50% of total radioactivity. At later time points, the pattern shifted in favor of NNK detoxification products (60-70% of total radioactivity in urine), mainly 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its O-glucuronide conjugates. One female rhesus monkey received a single i.v. dose of [5-3H]NNK (1.72 mCi; 28.4 microg/kg) under isoflurane anesthesia; biliary excretion over 6 h (0.6% of the dose) was 10 times less than predicted by our previously reported rat model. No preferential excretion of NNAL glucuronide was observed in monkey bile. Collectively, these results suggest that the rhesus monkey could be a useful model for NNK metabolism and disposition in humans.

Studies on pyrazinoylguanidine. 7. Effects of single oral doses in normal human subjects

In a three-phase study, single oral doses of placebo, followed in 1 week by pyrazinoylguanidine (PZG; 900 mg), followed in 3 weeks by pyrazinoic acid (PZA; 300 mg) were given to 8 normal male subjects. Blood analyses performed 0, 2 and 4 h after administration of placebo or drug revealed that compared to mean 0 h values, PZG and also PZA, but not placebo, decreased mean values for serum glucose, insulin, C-peptide, triglycerides and free fatty acids. In all groups, serum potassium, urea, fibrinogen, high-density lipoprotein and low-density lipoprotein were unchanged. PZA, but not PZG, increased serum uric acid. PZG significantly reduced very-low-density lipoprotein whereas PZA only tended to do so. PZG was well tolerated and without any side effect, but in 7 of the 8 normal volunteers, PZA produced a variable vasomotor response over the blush area of the face and neck lasting from 30 min in 3 subjects to 4 h in 1 subject. Collectively, these results suggest generally similar metabolic responses of normal subjects to PZG and PZA after only a single oral dose of each. Previously, it was unrecognized that acute administration of PZG and PZA could produce such rapid metabolic changes.

Pyrazinoylguanidine in end-stage renal disease: a prospective, placebo-controlled pilot study

Cardiovascular disease is the leading cause of mortality in end-stage renal disease (ESRD) patients receiving dialysis. In these patients, hypertriglyceridemia appears to increase the risk of accelerated atherosclerosis. The present placebo-controlled study evaluated prospectively lipid-lowering effects of pyrazinoylguanidine (PZG) in 6 ESRD patients undergoing maintenance hemodialysis. The design of the study entailed a placebo phase of 1 week followed by 3 weeks of PZG, 400 mg three times a day. Compared to placebo, PZG reduced serum triglycerides (PZG vs. placebo 370 +/- 171 vs. 414 +/- 182 mg/dl; p = 0.01). PZG also tended to decrease total cholesterol. In addition, PZG selectively lowered blood glucose in hyperglycemic patients. PZG was well tolerated; it did not interfere with hemodynamic parameters or alter liver function tests, nutritional parameters or dialysis clearance.

Pedigree analysis of a subject with abnormally slow renal elimination of 6-hydroxychlorzoxazone

The family of an unusual subject was studied. When tested with chlorzoxazone (CX; 250 mg p.o.) on four separate occasions 5 years ago, this subject showed abnormally slow renal elimination of 6-hydroxychlorzoxazone (HCX), the primary CX metabolite. Since rates of CX biotransformation to HCX have served as a probe of the important cytochrome P450 isozyme, CYP 2E1, it was of interest that this unusual subject had normal conversion of CX to HCX. The present study revealed that over the past 5 years this subject accelerated his renal rate of HCX elimination which now lies at the slow end of the curve for normal subjects. His wife and 5 children all had more rapid rates than he for renal HCX elimination.

Studies on pyrazinoylguanidine. 5. Temporal effects over 24 weeks demonstrating attenuation of diabetic nephropathy in STZ-diabetic rats

This study was designed to determine whether pyrazinoylguanidine (PZG) can attenuate diabetic nephropathy in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced within 1 week after a single intraperitoneal dose of STZ (45 mg/kg in 0.05 mol/l sodium citrate buffer). Diabetic rats were divided into five groups. Each group received by gavage for 24 weeks one of the following: vehicle (saline 10 ml/kg, b.i.d.), PZG (35 mg/kg, b.i.d.), captopril (15 mg/kg, b.i.d.), or hydrochlorothiazide (HCTZ, 20 mg/kg, b.i.d.). Insulin (NPH 7.5 U/day) was given subcutaneously. PZG treatment for 24 weeks reduced mortality and attenuated diabetic nephropathy, as indicated by reduced urinary excretion of total protein (79% of control), low-molecular-weight protein (12% of control), and albumin (60% of control). PZG also preserved renal structure and function. Compared to HCTZ or vehicle-treated rats, STZ-diabetic rats receiving either captopril or insulin exhibited decreased excretion of total protein, low-molecular-weight protein, and albumin, as well as amelioration of renal pathology. Collectively, these results indicate that PZG, as well as captopril and insulin, improved longevity and several indices of diabetic nephropathy in STZ-diabetic rats.

Studies on pyrazinoylguanidine. 6. Prevention of cataracts in STZ-diabetic rats

This study was designed to determine whether pyrazinoylguanidine (PZG) can attenuate cataract development in streptozotocin (STZ)-induced diabetic rats. After a single, intraperitoneal dose of STZ (45 mg/kg in 0.05 mol/l sodium citrate buffer), Sprague-Dawley rats (250-260 g) were divided into three groups. Beginning a week later, each group of diabetic rats received twice daily for 24 weeks by gavage one of the following: vehicle (saline 10 ml/kg), PZG (35 mg/kg), or captopril (15 mg/kg). PZG treatment prevented the development of diabetic cataracts (p = 0.0009 compared to vehicle). In contrast to PZG, 38% of vehicle-treated rats exhibited cataracts after 12 weeks, increasing to 89% after 16 weeks. At week 16, 22% of captopril-treated rats exhibited cataracts, a 75% reduction from vehicle-treated rats (p = 0.4289 compared to vehicle; p = 0.0571 compared to PZG). These results indicate that captopril can attenuate cataract formation in STZ-diabetic rats, whereas PZG completely suppresses it.

Acetylator phenotype in relation to age and gender in the Baltimore Longitudinal Study of Aging

This study investigated in healthy Caucasians the possible occurrence of age and gender-associated differences in NAT2 acetylator phenotype. Acetylator phenotype was determined after a single oral dose of 100 mg dapsone during testing of oral glucose tolerance in 510 Caucasian volunteers aged from 19 to 93 years, 339 men and 171 women, from the Baltimore Longitudinal Study of Aging. Participants were classified as slow or rapid acetylators according to the ratio of monoacetyldapsone to dapsone concentration in plasma. The ratio dividing the two groups, 0.30, was chosen after inspection of a probit plot and histogram of the monoacetyldapsone/dapsone ratios. Fifty-one percent of the participants were slow acetylators and 49% were rapid acetylators. Because there was no significant difference between the sexes in the monoacetyl-dapsone/dapsone ratios, all 510 participants were pooled into a single group for further analysis. In the combined analysis, there was a small decline in the prevalence of the slow acetylator phenotype with age, but this age effect accounted for less than 1% of the total variance in the monoacetyldapsone/dapsone ratio (r2 = 0.009). Also, it was shown in a group of 20 participants that administration of glucose with dapsone does not influence the determination of acetylator phenotype. In a large healthy Caucasian. American population, there was no biologically important effect of age or sex on the distribution of NAT2 acetylator phenotype.

Reflections from distant cuvettes

The main events described in this essay occurred between 30 and 40 years ago. Care has been exercised to describe these events as accurately as possible. I have confined myself to the facts as best I can recollect them now. I have also attempted to recapture the spirit and ambiance of the individual laboratories, their directors, and the scientists working there, leaving philosophical interpretations to others. I feel privileged to have been permitted to work in these laboratories and with these scientists. Despite present difficulties besetting those who desire to devote their lives to scientific research, I encourage these hardy souls to pursue their vision and wish for them the good fortune I had in being associated with so many supportive, brilliant, and interesting researchers.

Studies on pyrazinoylguanidine. 4. Upregulation of phosphodiesterase activity in rat adipose tissue and downregulation of gluconeogenesis and adenosine 3',5'-monophosphate concentrations in perfused rat liver

In isolated rat adipocytes stimulated with theophylline (1 mmol/l), pyrazinoylguanidine (PZG) downregulated both lipolysis and cyclic AMP concentrations, raising the possibility that PZG stimulates adipose insulin-sensitive phosphodiesterase. To investigate this directly, we measured PZG's effects on phosphodiesterase activity in rat adipocytes. PZG (10 mumol/l) as well as insulin (0.1-1 mU) increased adipose phosphodiesterase activity, whereas theophylline reduced it. Also investigated were PZG's effects on gluconeogenesis and cyclic AMP in perfused rat liver where PZG decreased gluconeogenesis and cyclic AMP concentrations.

Studies on pyrazinoylguanidine. 3. Downregulation of lipolysis in isolated adipocytes

The effects of pyrazinoylguanidine (PZG) on lipolysis and intracellular cyclic AMP concentrations were investigated in isolated rat adipocytes. PZG reduced basal cyclic AMP concentrations and blocked in a concentration-dependent manner forskolin (1 mumol/l) and isoproterenol (1 mumol/l) stimulatory effects on intracellular cyclic AMP production and lipolysis. PZG's effects on hormone-sensitive lipase were investigated in the presence and absence of glucagon (1 mumol/l) or isoproterenol (1 mumol/l). PZG inhibited uncompetitively the induction of hormone-sensitive lipase by either glucagon or isoproterenol. PZG's antilipolytic effects appeared to result from downregulation of intracellular cyclic AMP concentrations. In adipose tissue, cyclic AMP controls lipolysis through hormone-sensitive lipase. PZG's downregulation of lipolysis and cyclic AMP concentrations was unaffected by adenosine deaminase or pertussis toxin, suggesting that PZG did not activate Gi, the inhibitory guanyl nucleotide regulatory protein.

Studies on pyrazinoylguanidine. 2. Comparative drug and dose effects on glucose and lipid metabolism in streptozotocin-induced diabetic rats

In streptozotocin (STZ)-induced diabetic rats, pyrazinoylguanidine (PZG) markedly reduced elevated fasting concentrations of plasma glucose, triglycerides, and cholesterol. In contrast, these parameters were unaffected by a sulfonylurea, glyburide, or by a biguanide, metformin. PZG's glucose- and lipid-lowering effects were dose-dependent. These metabolic effects were also investigated after: (a) pyrazinoic acid (PZA), a metabolite of PZG; (b) 3-amino-PZG, an analog of PZG, and (c) 3-amino-PZA, a hydrolytic product of 3-amino-PZG. PZA moderately reduced elevated fasting glucose and lipid concentrations in STZ-diabetic rats, suggesting partial medication of PZG's antidiabetic actions by PZA. Neither 3-amino-PZG nor 3-amino-PZA exerted any glucose- or lipid-lowering effect in STZ-diabetic rats.

Studies on pyrazinoylguanidine. 1. Characterization of metabolic effects in diabetic rats

Pyrazinoylguanidine (PZG) is a new antihyperglycemic, antihyperlipidemic drug. The current study reports on the development of an animal model in which the favorable metabolic effects of PZG, previously described in diabetic patients, could be reproduced and investigated. Adult male as well as female Sprague-Dawley rats received a single intraperitoneal dose (50 mg/kg) of streptozotocin (STZ). One week later, they received PZG (50 mg/kg i.p.) twice daily for a week. Compared to vehicle (saline-treated controls), PZG reduced plasma concentrations of glucose by 33-70%, triglycerides by 50-70%, nonesterified fatty acids by 17-27%, cholesterol by 10-50%, and glucagon by 18-20%. Hydrochlorothiazide given in a dose of 20 mg/kg i.p. b.i.d for 1 week induced metabolic effects opposite to those of PZG. In the Zucker fatty rat, PZG also lowered plasma glucose and lipid concentrations. These results indicate that PZG ameliorated the abnormalities of plasma glucose and lipid that characterize STZ-diabetic and Zucker fatty rats.

Pyrazinoylguanidine downregulates the glucose fatty-acid cycle in hypertensive, hyperinsulinemic diabetic patients

Eight hypertensive patients with noninsulin dependent diabetes mellitus (NIDDM) were administered the experimental drug pyrazinoylguanidine (PZG) either alone or in combination with calcium-channel or beta-blockers. This treatment appeared to "downregulate" the glucose fatty acid cycle and reduced both systolic and diastolic blood pressures and mean body weight. Patients served as their own controls in this dose-escalation study, which included placebo treatment (baseline) 3 weeks, 300 mg PZG for 3 weeks and 600 mg for 3 weeks. PZG reduced increased serum concentrations of free fatty acids (FFA), glucose, and triglycerides (TG). TG concentrations correlated inversely with serum HDL-cholesterol concentrations. The beta-blockers used by several patients increased their FFA, glucose, insulin and TG concentrations, as well as blunting their response to PZG. The calcium-channel blockers exerted these effects to a much lesser extent. PZG reduced or abolished glycosuria, related to PZG's capacity to decrease hyperglycemia. Withdrawal of PZG restored glycosuria, as blood sugar increased. PZG was well tolerated. No patient reported any adverse effect or missed a weekly clinic visit (12 weeks). PZG deserves further study as supplementary and/or replacement therapy in NIDDM patients who are hypertensive and hyperlipidemic.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Identification of radiolabeled metabolites of nicotine in rat bile. Synthesis of S-(-)-nicotine N-glucuronide and direct separation of nicotine-derived conjugates using high-performance liquid chromatography

Four metabolites of nicotine, including two glucuronides, have been separated by high-performance liquid chromatography. This separation was applied to identification of biliary metabolites of radiolabeled nicotine by radiometric detection. S-(-)-Nicotine N-glucuronide was synthesized and used as a standard in method development.

Effects of pyrazinoylguanidine on the glucose-fatty acid cycle in normal subjects and patients with non-insulin-dependent diabetes mellitus

Pyrazinoylguanidine (PZG) reduced the hyperglycemia, hyperinsulinemia, and hyperlipidemia of patients with non-insulin-dependent diabetes mellitus (NIDDM) as well as of normal subjects receiving hydrochlorothiazide (HCTZ). Mechanisms are proposed by which PZG downregulated the elevated glucose-fatty acid cycle toward a more normal level in NIDDM patients and in non-diabetic subjects maintained on HCTZ. Despite maintenance of these NIDDM patients on their current antihypertensive medication, PZG reduced further their systolic and diastolic pressures. PZG was well tolerated by both normal and NIDDM patients.

Rates of excretion of cotinine, nicotine glucuronide, and 3-hydroxycotinine glucuronide in rat bile

A new HPLC assay was adapted for radiometric detection of nicotine metabolites in rat bile. Two glucuronides were identified as the principal biliary metabolites of nicotine. In addition to nicotine glucuronide and 3-hydroxycotinine glucuronide, cotinine was also detected in bile after administration to rats of a single subcutaneous dose of (-)-S-nicotine (0.2 or 1.0 mg/kg) that contained a tracer dose of rac-[pyrrolidine-2'-14C]nicotine (20 microCi). Biliary metabolites accounted for only 3% of the [14C]nicotine dose, but phenobarbital pretreatment (100 mg/kg ip for 3 days) increased the amount of [14C]nicotine-derived radioactivity recovered in bile to 8% and also accelerated rates of biliary excretion of all three nicotine metabolites. Dose-dependency of nicotine metabolism occurred: less nicotine glucuronide was excreted at the low dose than at the high dose.

Reproducibility of antipyrine half-lives in elderly subjects

Antipyrine half-life determined on three to five separate occasions over a period ranging from 3 weeks to 1 year was highly reproducible in each of 20 elderly subjects (12 women and 8 men; mean age, 83 years). The mean within-subject coefficient of variation for antipyrine half-life was 9.6%, whereas the between-subject coefficient of variation was 33.3%. These findings indicate high reproducibility of individual rates of drug metabolism in medically stable elderly subjects.

Contrasting effects of pyrazinoylguanidine and hydrochlorothiazide in patients with renal insufficiency

A single blind crossover study with washout phases showed that pyrazinoylguanidine (PZG) reduced elevated serum concentrations of urea, triglycerides, and cholesterol in patients with renal insufficiency. Pyrazinoylguanidine was saluretic, without affecting serum potassium or glucose concentrations. The onset of PZG's antihypertensive effect occurred within 4 hours. In contrast, hydrochlorothiazide (HCTZ) increased serum concentrations of urea, triglycerides, and glucose, without affecting cholesterol.

Pyrazinoylguanidine: antihypertensive, hypocholesterolemic, and renin effects

In a single-blind, placebo-controlled study of 12 subjects diagnosed as having mild to moderate hypertension and hypercholesterolemia, pyrazinoylguanidine (PZG) in a dose of 600 mg twice daily for 4 weeks reduced systolic blood pressure and heart rate. Pyrazinoylguanidine also reduced diastolic pressures, but to a lesser extent. Pyrazinoylguanidine reduced total serum cholesterol and low-density lipoprotein (LDL). Regression analysis indicated a dose-dependent reduction of both total cholesterol and LDL by PZG, i.e., the higher the presenting serum concentration, the greater the reduction by PZG. The extent of the reductions produced by PZG in elevated cholesterols and LDLs was highly correlated (r = .949). Normal high-density lipoprotein levels were unchanged by PZG. Pyrazinoylguanidine increased 24-hour urine volume and urinary excretion of sodium. Serum Na+, K+, or Cl- concentrations were unaltered. Means for plasma aldosterone and renin activities tended to decrease, but these trends did not attain statistical significance. Pyrazinoylguanidine was well tolerated. An activity profile that includes antihypertensive effects as well as reduction in hypercholesterolemia without major impact on serum renin or electrolyte balance makes PZG an attractive candidate for the management of hypertension.

Hormonal and immunological regulation of 2', 5'-oligoadenylate synthetase activity in human peripheral blood mononuclear cells

A newly developed method for assaying 2', 5'-oligoadenylate (2, 5A) synthetase activity by polyacrylamide gel electrophoresis was applied to peripheral blood mononuclear cells (PBMC) from normal subjects, HIV-positive subjects, and renal cell carcinoma (RCC) patients. Sex differences were observed in 2, 5A synthetase activity of PBMC from normal young adults, males having eightfold higher activities of this enzyme than females. Moreover, compared to values for postmenopausal (PM) females receiving estrogen replacement, untreated PM females had higher activities. Collectively, these results suggest that estrogen downregulates 2, 5A synthetase activity. Activities of 2, 5A synthetase were investigated in two disease states associated with altered immune function. In one patient with AIDS-related Kaposi's sarcoma, interferon-alpha (IFN-alpha) therapy increased 2, 5A synthetase activity twofold. In addition, combined therapy with interleukin-2 (IL-2) and IFN-alpha increased 2, 5A synthetase activities in eight of nine patients with RCC. Therefore, in patients receiving immunotherapy with IL-2 and IFN-alpha, our new assay could contribute to evaluation of immune stimulation. In general, studies in vitro confirmed these observations; however, exposure of PBMC from RCC patients revealed that in vitro IL-2 failed to induce this enzyme activity as it did in PBMC from normal volunteers.

Do histocompatibility antigens antigence influence the risk of head and neck carcinoma?

Associations were sought between specific histocompatibility antigens (HLA) of the human major histocompatibility complex and the incidence of head and neck squamous cell carcinoma (SqCC). Seventy sequential patients with SqCC and 217 control subjects from the same geographic region were typed for HLA-A, HLA-B, and HLA-DR loci. These results were compared. Multivariate statistical analysis using stepwise logistic regression revealed significant associations between the incidence of SqCC and HLA-B14, HLA-DR3, and HLA-DR4 as well as smoking and the sex-smoking interaction. The authors concluded that certain host factors, including genetic constitution, and behavioral characteristics (i.e., smoking) as well as tumor biology, can influence the development of SqCC. The mechanism(s) of these associations may involve as yet undefined relationships between HLA region genes and the immune response.

Pharmacokinetics of pyrazinoyl-guanidine, 3-aminopyrazinoyl-guanidine and their corresponding pyrazinoic acid metabolites in humans and dogs

Pyrazinoylguanidine (PZG), 3-aminopyrazinoylguanidine (NH2PZG) and their pyrazinoic acid metabolites were measured by a new reverse-phase HPLC method in the serum of dogs and humans after administration of PZG, NH2PZG or 2-pyrazinoic acid (PZA). Kinetic properties of PZG and its principal metabolite, PZA, were studied in normal humans and also in azotemic patients, since PZG acts on renal tubules of patients with kidney failure to increase urea elimination. In humans and dogs, PZG was rapidly hydrolyzed to PZA. The serum half-life (t1/2) of PZG was 1 h. In turn, PZA was metabolized to 5-hydroxy-PZA, but no evidence appeared for conjugation of PZA with glycine. The apparent volume of distribution of PZG and its 3-amino analog, NH2PZG, exceeded that of total body water. In the dog the serum t1/2 for NH2PZG was twice that of PZG. Compared to PZG, NH2PZG and its metabolite, 3-aminopyrazinoic acid, were much stabler in vitro in serum and water.

Inhibition of urea transport across renal tubules by pyrazinoylguanidine and analogs

In addition to glomerular filtration and passive back diffusion of urea, there occurs across the renal tubule bidirectional transport of urea inhibitable in one or both directions by specific analogs of pyrazinoylguanidine (PZG). Effect of PZG on the profiles of sodium and urea concentrations along the tubule (stop flow) are consistent with their independent transport. Inhibition of urea and sodium reabsorption by PZG is dose dependent. PZG does not inhibit potassium excretion.

Nicotine metabolism in stumptailed macaques, Macaca arctoides

Stumptailed macaques received a single i.v. dose of 14C-nicotine (5 microCi and 300 micrograms/kg) on several separate occasions to establish baselines. Then they were pretreated with phenobarbital (2.0 mg/kg/day im for 7 days) and 8 weeks later pretreated with cimetidine (8.5 mg/kg/day im for 4 days). Nicotine in the same dose as before was readministered after each pretreatment. The baseline pattern of nicotine metabolism observed in plasma and urine, highly reproducible within and between macaques, closely resembled that previously reported in humans using GC and HPLC analysis. In urine, nicotine and eight metabolites were identified, including high concentrations of metabolites A and G. Recently discovered in humans, metabolites A and G are of special interest for their long duration in the body. Phenobarbital pretreatment accelerated rates of production of all nicotine metabolites except nornicotine and nicotine-1'-N-oxide, whereas cimetidine retarded rates of production of five metabolites. Sex differences in nicotine metabolism resembled those reported in humans. Collectively, these results suggest that the stumptailed macaque may be a useful model for certain aspects of nicotine metabolism in humans.

HLA antigens influence resistance to lung carcinoma

The concept of genetic factors playing a role in the pathogenesis of lung cancer has gained increased attention. The present study was undertaken to reexamine the question of HLA antigen association with carcinoma of the lung. In a study of 90 patients, a significant association occurred between HLA-DR7 and resistance to lung cancer, after accounting for smoking status and sex. HLA class I antigens were also implicated. These results suggest that major histocompatibility complex loci affect carcinoma of the lung.

Diet and cimetidine induce comparable changes in theophylline metabolism in normal subjects

This study compared the effects of diet and cimetidine on theophylline metabolism and examined interactions between these effects. Twelve men received a high-protein diet for 15 days and at another time a high-carbohydrate diet also for 15 days. Cimetidine, 800 mg daily at bedtime, was administered on days 10 through 15 of each dietary period. Theophylline metabolism was studied after the administration of a single intravenous 3 mg/kg dose on days 8 and 15 of each dietary period. Changing from a high-protein to a high-carbohydrate diet decreased theophylline clearance by about the same extent (30% +/- 10%) as treatment with cimetidine (37% +/- 5% during a high-protein diet and 30% +/- 5% during a high-carbohydrate diet). Cimetidine did not significantly influence the effects of diet on theophylline clearance. Conversely, dietary composition did not influence the degree of inhibition of theophylline metabolism induced by cimetidine. Depending on the direction of the change in protein/carbohydrate ratio, the effects of diet and cimetidine treatment were either additive (theophylline clearance was most prolonged during the high-carbohydrate regimen with concurrent cimetidine administration) or counteractive (increasing the dietary protein/carbohydrate ratio at least partially counteracted the inhibitory effect of cimetidine). In individual subjects, effects of cimetidine on theophylline metabolism were somewhat more consistent than diet-induced changes. The results are further evidence that diet and drugs can have similar effects on hepatic drug metabolism rates in humans. Variations in diet over time and individual differences in responses to diet may provide the potential for considerable instability of drug metabolism rates in free-living subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic and environmental factors causing variation in drug response

Large pharmacokinetic variations, ranging in magnitude from 4- to 40-fold, often exist among the members of a given population. These variations create differences in risk of cancer by accelerating metabolic activation of certain environmental carcinogens in some subjects, while retarding such rates in other subjects. To identify specific genetic and environmental causes of large interindividual variations in these rates, several methods have been developed to probe hepatic cytochrome P-450 isozymes responsible for xenobiotic activation. In patients, dynamic interactions occur between genetic and environmental factors causing large interindividual variations in xenobiotic metabolism. Even the same patient can change dosage requirements with time and condition. Appropriate marker drugs can sensitively indicate pharmacokinetic capacity at any given time in a patient or normal volunteer. With respect to genetic factors, twin and family studies are the traditional methods used to test pharmacogenetic hypotheses. Representative examples are cited to illustrate how twin and family studies serve this purpose. Monogenic control of large interindividual variations in the activity of approx. 12 P-450 isozymes has been described. Individual metabolic pathways need to be investigated for drugs biotransformed by multiple pathways. Since many hepatic P-450 isozymes are extremely sensitive to perturbation by numerous environmental alterations, the critical role of selection criteria is stressed to assure that all subjects of twin and family studies are under as uniform environmental conditions as possible. Otherwise, the operation of genetic factors may be concealed or misinterpreted in studies that do not use gene cloning or protein sequence.

Disposition of nicotine and eight metabolites in smokers and nonsmokers: identification in smokers of two metabolites that are longer lived than cotinine

The disposition of a single intravenous dose of 14C-nicotine was investigated in six cigarette smokers and six nonsmokers. Plasma and urinary elimination of both nicotine and cotinine was faster in smokers than in nonsmokers. In the urine of both smokers and nonsmokers, we identified nicotine and eight metabolites, including two new metabolites: metabolite A (3-hydroxycotinine glucuronide) and metabolite G (demethylcotinine delta 2',3'-enamine). Metabolites A and G were of particular interest because, in smokers, they both persisted longer than cotinine. This property renders them more sensitive than cotinine as potential indicators of passive exposure to cigarette smoke.

Metabolism of nicotine by hepatocytes

The profile of nicotine metabolites produced by freshly isolated hepatocytes from rats, hamsters, guinea pigs, mice and humans was investigated after a 30-min exposure to nicotine ([2-14C]pyrrolidine). Large species differences occurred in the extent of nicotine metabolism; these ranged from 95% metabolism in guinea pig hepatocytes to only 30% metabolism in human and rat hepatocytes. The spectrum of metabolites formed also varied widely in different species. In hepatocytes from obese human subjects, nicotine was metabolized most extensively in smokers, least in nonsmokers, and to an intermediate degree in exsmokers, suggesting that cigarette smoking enhances the rate of nicotine metabolism. Pretreatment of all nonhuman species studied with phenobarbital and beta-naphthoflavone and with Aroclor in rats produced distinctive inductive patterns. Phenobarbital pretreatment of nonsmokers for 2 days prior to liver biopsy doubled the extent of nicotine conversion to cotinine by their hepatocytes. Rat and hamster hepatocytes exhibited sex and stereoselectivity differences in nicotine metabolism. Collectively, these studies indicate that hepatocytes offer some advantages over in vivo systems in investigating certain aspects of nicotine metabolism.

A new quantitative thermospray LC-MS method for nicotine and its metabolites in biological fluids

A rapid thermospray liquid chromatography-mass spectrometry (TSP LC-MS) method is described for the simultaneous determination of nicotine and 17 of its metabolites. Chemical ionization of nicotine and its metabolites separated by reversed-phase HPLC is achieved by postcolumn addition of ammonium acetate buffer with the filament of the ion source turned off. Quantification is accomplished by selectively monitoring the unique protonated molecular ion of each metabolite. Trideuterated cotinine serves as an internal standard. Linear responses for cotinine, demethylcotinine, and trans-3'-hydroxycotinine were observed over a concentration range of 20-8000 ng/mL, and 80-8000 ng/ml for nicotine and nicotine-1'-N-oxide. Of the 17 metabolites examined, only nicotine, cotinine, demethylcotinine, and trans-3'-hydroxycotinine were detected in smokers' urine.