112
Proc. roy. Soc. Med. Volume 691976 Supplement 2
Preliminary Observations on the Effect of Gemfibrozil on the Excretion of Fiecal Bile Acids by Dr I McLean Baird, Professor B Lewis and Dr J M Hill (West Middlesex and St Thomas's Hospitals and Central Public Health Laboratory, Colindale Hospital, London, UK) Nine non-obese patients with hyperlipidmmia were studied on a regime of six weeks' placebo and 26 weeks' gemfibrozil in a dosage of 1200 mg daily. No side effects attributable to the drug were seen. A lowering of the mean plasma triglyceride and plasma cholesterol levels was observed which was most marked in the higher ranges, but this was not consistent, particularly at the lower range of
Dr I McLean Baird
Table I Excretion of facal bile acids (FBA) in patients receiving gemfibrozil
Totalftcal bile acids Facalfats (g/day)
(mg/day) Subject Age 1 54 2
48
3
45
Sex Placebo M 500 (12.1) M 557 (13.3) M 346
(11.6)
Gemfibrozil Placebo 5.78
349 (11.0) 454 (11.1) 358 (10.4)
Gemfibrozil Effect 2.69 Total FBA
6.28
4.23
2.56
2.84
lowered Total FBA lowered No change
Concentration of FBA (mg/g) shown in parentheses
triglyceride and cholesterol. Preliminary observations on the excretion of fmcal bile acids showed a fall in 2 out of 3 patients (Table 1) on gemfibrozil when compared with the placebo. Clofibrate is known to induce lithogenic bile and causes a fall in fecal bile acids and raised neutral steroids (Pertsemlidis et al. 1974), and the effects of gemfibrozil are being studied further.
The practical implications of changes in biliary kinetics lie in the future development of gallstones in patients on long-term hypolipidmmic drugs. REFERENCE Pertsemlidis D, Panvelliwalla D & Ahrens E H (1974) Gastroenterology 66, 565
Gemfibrozil DISCUSSION Professor B Lewis (Chairman) agreed with Dr Rasi's reservations about long-term drug use. There were demonstrated differences between the laboratory effects of clofibrate and the apparent effect which it showed in the Drug Heart Study in the United States in which there appeared to be an increase in thrombotic events such as deep vein thrombosis. It was therefore essential to look at gemfibrozil in the long term as well. Dr R E Maxwell (Ann Arbor) asked Professor Carlson what general conclusions could be drawn from his experiments with human adipose tissue.
Professor Carlson said that two general statements could be made. The first was that to observe an inhibition of lipolysis in human fat with either clofibrate or gemfibrozil under in vitro conditions, high doses were needed, in the order of 1000,ug/ml. Secondly, it was impossible to predict from one case to the next whether there would be an effect or not. In some experiments there was no inhibition of lipolysis either under basal or noradrenaline-stimulated conditions. This contrasted with the situation using rat fat, in which a predictable result might be obtained. Dr Kissebah said it was well known that the response of human adipose tissue was variable. The variation depended upon two main factors. The first was the dietary situation of the patient at the time of biopsy. The second was the need for a high dose of any agent to demonstrate an effect. An antilipolytic effect of insulin which was quite obvious in any animal species, required 10 mU of insulin in human adipose tissue. He thought that Professor Carlson's work would have profited from the incorporation of a natural antilipolytic agent such as insulin to measure the sensitivity of the tissue during his experiments. In answer to a question from Dr Ghosh, Dr Kissebah agreed that his FFA kinetic studies were based on four patients. The kinetic approach was extremely time-consuming, and the consistency of the results suggested that they were acceptable, at this stage at least.
113
though they still remained high and were not returned to normal he was still concerned with the two possible mechanisms for this reduction. One possibility was an inhibition of lipolysis in adipose tissue. The second was a decrease of FFA secondary to the decrease in triglycerides, since a lot of the plasma FFA originated from the turnover of high plasma triglyceride levels. He asked whether the effect was secondary to a decrease in triglycerides or whether it was a primary effect mediated through the adipose tissue. Dr Kissebah said that in their previously published work on the turnover of fatty acid and its relation to triglycerides in normal and hypertriglyceridwmic subjects, they had not observed a significant difference between these groups in respect of recycling from the plasma unless the patients were given heparin or some other agents to raise lipoprotein lipase. He therefore felt the drug had a primary effect on lipolysis. At this stage the nature of the derangement of lipolysis in endogenous hypertriglycerid&mia was still unknown. Was it actually lipolysis or was it re-esterification? When using clofibrate he had observed that the higher the flux the better the effect. If the patient started with a high turnover then he saw a marked reduction, but the patient with a marginally elevated level showed no effect. Therefore the effect was not a direct one of the drug on the adipose tissue. It was probably more complicated than simple inhibi-
tion of lipolysis. Professor Lewis asked, since all Dr Kissebah's patients were obese, around 130% of ideal body weight, whether there was a correlation between the FFA flux and their weight excess. Dr Kissebah said that even with larger groups of patients with endogenous hypertriglyceridwmia he saw no such correlation. It was possible to segregate the endogenous hypertriglyceridaemic patients into those above and those below 130% of ideal weight. A difference was then seen between the groups, but within each group there was no correlation.
Professor Lewis said that these patients were heterogeneous in terms of their serum lipid responses, and he hoped that Dr Kissebah's group would study larger numbers of patients in due course.
Professor Lewis asked whether among the substantial number of patients with whom he had worked, Dr Kissebah felt that the raised FFA turnover was a reflection of the increased adipose tissue mass or whether he thought it to be a specific feature of the hypertriglyceridcemia.
Professor E A Nikkila (Helsinki) said that plasma FFA levels seemed to be reduced during gemfibrozil treatment in Dr Kissebah's patients. Even
Dr Kissebah believed that it was a specific feature. Other workers had investigated the fat cells from a number of these individuals, and it
114 Proc. roy. Soc. Med. Volume 69 1976 Supplement 2
seemed the pattern of lipolysis and response to insulin and other hormones was completely different from those of normal individuals, irrespective of weight. Professor Lewis noted that in Dr Kissebah's work, as in his own, the proportion of VLDL label appearing in LDL in normal individuals was of the order of 90% or more, while in individuals with an increased VLDL concentration, the turnover of VLDL was in most cases increased. It seemed that in those individuals with a high input of VLDL into the circulation, perhaps up to half of the VLDL disappeared by some unidentified extravascular pathway. Dr Kissebah had now shown that this was not a direct catabolic pathway. The radioactive label did not appear in the urine. Dr Kissebah said that he had been prompted by Professor Lewis's original finding to examine the urine every two hours in an attempt to account for this 50% of the turnover. Knowledge of the two pathways might explain a great deal about lipogenesis. Something appeared in the urine, but it was certainly not the total quantity. The effect, though unexplained, was valid and certainly not an artefact.
He asked Dr Galton if anyone had investigated the dose-response curve of isolated lymphocytes and isolated liver cells to see whether the lymphocyte is of any biological significance to the major
synthetic organ, that is the liver, with regard to cholesterol metabolism. Dr Galton said that he was using the leukocyte only as a convenient human cell marker for pathways of cholesterol synthesis. The liver was a less accessible tissue, although the regulation of the enzyme in leukocytes seemed to resemble that in fibroblasts, which may well resemble the situation in the liver itself. Nonetheless, he agreed that it would be worth establishing whether rat lymphocytes, for example, responded with a similar pattern as did liver cells. He also stated, for the record, that he was using total leukocytes and not lymphocytes. Professor Wynn drew attention to the change in the excretory pattern of cholesterol towards neutral sterol excretion and away from bile acid excretion under the influence of both clofibrate and gemfibrozil. Such a change may represent a very fundamental alteration in the catabolic pathway. Animal, though apparently not human, results showed significant changes in the histology of the liver, with a great increase in the smooth endoplasmic reticulum and the accumulation of microbodies. If that endoplasmic reticulum were hypoactive, as it was under the influence of many cholestatic drugs, this might explain the excretion of cholesterol in preference to bile acids. Other possible mechanisms existed, including an alteration in bile flow, since bile acid secretion was very much dependent on the rate of bile secretion.
Proc. roy. Soc. Med. Volume 691976 Supplement 2
Preliminary Observations on the Effect of Gemfibrozil on the Excretion of Fiecal Bile Acids by Dr I McLean Baird, Professor B Lewis and Dr J M Hill (West Middlesex and St Thomas's Hospitals and Central Public Health Laboratory, Colindale Hospital, London, UK) Nine non-obese patients with hyperlipidmmia were studied on a regime of six weeks' placebo and 26 weeks' gemfibrozil in a dosage of 1200 mg daily. No side effects attributable to the drug were seen. A lowering of the mean plasma triglyceride and plasma cholesterol levels was observed which was most marked in the higher ranges, but this was not consistent, particularly at the lower range of
Dr I McLean Baird
Table I Excretion of facal bile acids (FBA) in patients receiving gemfibrozil
Totalftcal bile acids Facalfats (g/day)
(mg/day) Subject Age 1 54 2
48
3
45
Sex Placebo M 500 (12.1) M 557 (13.3) M 346
(11.6)
Gemfibrozil Placebo 5.78
349 (11.0) 454 (11.1) 358 (10.4)
Gemfibrozil Effect 2.69 Total FBA
6.28
4.23
2.56
2.84
lowered Total FBA lowered No change
Concentration of FBA (mg/g) shown in parentheses
triglyceride and cholesterol. Preliminary observations on the excretion of fmcal bile acids showed a fall in 2 out of 3 patients (Table 1) on gemfibrozil when compared with the placebo. Clofibrate is known to induce lithogenic bile and causes a fall in fecal bile acids and raised neutral steroids (Pertsemlidis et al. 1974), and the effects of gemfibrozil are being studied further.
The practical implications of changes in biliary kinetics lie in the future development of gallstones in patients on long-term hypolipidmmic drugs. REFERENCE Pertsemlidis D, Panvelliwalla D & Ahrens E H (1974) Gastroenterology 66, 565
Gemfibrozil DISCUSSION Professor B Lewis (Chairman) agreed with Dr Rasi's reservations about long-term drug use. There were demonstrated differences between the laboratory effects of clofibrate and the apparent effect which it showed in the Drug Heart Study in the United States in which there appeared to be an increase in thrombotic events such as deep vein thrombosis. It was therefore essential to look at gemfibrozil in the long term as well. Dr R E Maxwell (Ann Arbor) asked Professor Carlson what general conclusions could be drawn from his experiments with human adipose tissue.
Professor Carlson said that two general statements could be made. The first was that to observe an inhibition of lipolysis in human fat with either clofibrate or gemfibrozil under in vitro conditions, high doses were needed, in the order of 1000,ug/ml. Secondly, it was impossible to predict from one case to the next whether there would be an effect or not. In some experiments there was no inhibition of lipolysis either under basal or noradrenaline-stimulated conditions. This contrasted with the situation using rat fat, in which a predictable result might be obtained. Dr Kissebah said it was well known that the response of human adipose tissue was variable. The variation depended upon two main factors. The first was the dietary situation of the patient at the time of biopsy. The second was the need for a high dose of any agent to demonstrate an effect. An antilipolytic effect of insulin which was quite obvious in any animal species, required 10 mU of insulin in human adipose tissue. He thought that Professor Carlson's work would have profited from the incorporation of a natural antilipolytic agent such as insulin to measure the sensitivity of the tissue during his experiments. In answer to a question from Dr Ghosh, Dr Kissebah agreed that his FFA kinetic studies were based on four patients. The kinetic approach was extremely time-consuming, and the consistency of the results suggested that they were acceptable, at this stage at least.
113
though they still remained high and were not returned to normal he was still concerned with the two possible mechanisms for this reduction. One possibility was an inhibition of lipolysis in adipose tissue. The second was a decrease of FFA secondary to the decrease in triglycerides, since a lot of the plasma FFA originated from the turnover of high plasma triglyceride levels. He asked whether the effect was secondary to a decrease in triglycerides or whether it was a primary effect mediated through the adipose tissue. Dr Kissebah said that in their previously published work on the turnover of fatty acid and its relation to triglycerides in normal and hypertriglyceridwmic subjects, they had not observed a significant difference between these groups in respect of recycling from the plasma unless the patients were given heparin or some other agents to raise lipoprotein lipase. He therefore felt the drug had a primary effect on lipolysis. At this stage the nature of the derangement of lipolysis in endogenous hypertriglycerid&mia was still unknown. Was it actually lipolysis or was it re-esterification? When using clofibrate he had observed that the higher the flux the better the effect. If the patient started with a high turnover then he saw a marked reduction, but the patient with a marginally elevated level showed no effect. Therefore the effect was not a direct one of the drug on the adipose tissue. It was probably more complicated than simple inhibi-
tion of lipolysis. Professor Lewis asked, since all Dr Kissebah's patients were obese, around 130% of ideal body weight, whether there was a correlation between the FFA flux and their weight excess. Dr Kissebah said that even with larger groups of patients with endogenous hypertriglyceridwmia he saw no such correlation. It was possible to segregate the endogenous hypertriglyceridaemic patients into those above and those below 130% of ideal weight. A difference was then seen between the groups, but within each group there was no correlation.
Professor Lewis said that these patients were heterogeneous in terms of their serum lipid responses, and he hoped that Dr Kissebah's group would study larger numbers of patients in due course.
Professor Lewis asked whether among the substantial number of patients with whom he had worked, Dr Kissebah felt that the raised FFA turnover was a reflection of the increased adipose tissue mass or whether he thought it to be a specific feature of the hypertriglyceridcemia.
Professor E A Nikkila (Helsinki) said that plasma FFA levels seemed to be reduced during gemfibrozil treatment in Dr Kissebah's patients. Even
Dr Kissebah believed that it was a specific feature. Other workers had investigated the fat cells from a number of these individuals, and it
114 Proc. roy. Soc. Med. Volume 69 1976 Supplement 2
seemed the pattern of lipolysis and response to insulin and other hormones was completely different from those of normal individuals, irrespective of weight. Professor Lewis noted that in Dr Kissebah's work, as in his own, the proportion of VLDL label appearing in LDL in normal individuals was of the order of 90% or more, while in individuals with an increased VLDL concentration, the turnover of VLDL was in most cases increased. It seemed that in those individuals with a high input of VLDL into the circulation, perhaps up to half of the VLDL disappeared by some unidentified extravascular pathway. Dr Kissebah had now shown that this was not a direct catabolic pathway. The radioactive label did not appear in the urine. Dr Kissebah said that he had been prompted by Professor Lewis's original finding to examine the urine every two hours in an attempt to account for this 50% of the turnover. Knowledge of the two pathways might explain a great deal about lipogenesis. Something appeared in the urine, but it was certainly not the total quantity. The effect, though unexplained, was valid and certainly not an artefact.
He asked Dr Galton if anyone had investigated the dose-response curve of isolated lymphocytes and isolated liver cells to see whether the lymphocyte is of any biological significance to the major
synthetic organ, that is the liver, with regard to cholesterol metabolism. Dr Galton said that he was using the leukocyte only as a convenient human cell marker for pathways of cholesterol synthesis. The liver was a less accessible tissue, although the regulation of the enzyme in leukocytes seemed to resemble that in fibroblasts, which may well resemble the situation in the liver itself. Nonetheless, he agreed that it would be worth establishing whether rat lymphocytes, for example, responded with a similar pattern as did liver cells. He also stated, for the record, that he was using total leukocytes and not lymphocytes. Professor Wynn drew attention to the change in the excretory pattern of cholesterol towards neutral sterol excretion and away from bile acid excretion under the influence of both clofibrate and gemfibrozil. Such a change may represent a very fundamental alteration in the catabolic pathway. Animal, though apparently not human, results showed significant changes in the histology of the liver, with a great increase in the smooth endoplasmic reticulum and the accumulation of microbodies. If that endoplasmic reticulum were hypoactive, as it was under the influence of many cholestatic drugs, this might explain the excretion of cholesterol in preference to bile acids. Other possible mechanisms existed, including an alteration in bile flow, since bile acid secretion was very much dependent on the rate of bile secretion.
