George A. Reichard

Nature and quantity of fuels consumed in patients with alcoholic cirrhosis.

Although alcoholism is a leading cause of morbidity and mortality of middle-aged Americans, there are no data available pertaining to the consequences of Laennecs cirrhosis on total body energy requirements or mechanisms for maintaining fuel homeostasis in this patient population. Therefore, we simultaneously used the techniques of indirect calorimetry and tracer analyses of [14C]palmitate to measure the nature and quantity of fuels oxidized by patients with biopsy-proven alcoholic cirrhosis and compared the results with values obtained from health volunteers. Cirrhotic patients were studied after an overnight fast (10-12 h). Normal volunteers were studied after an overnight fast (12 h) or after a longer period of starvation (36-72 h). Total basal metabolic requirements were similar in overnight fasted cirrhotic patients (1.05 +/- 0.06 kcal/min per 1.73 m2), overnight fasted normal subjects (1.00 +/- 0.05 kcal/min per 1.73 m2), and 36-72-h fasted normal volunteers (1.10 +/- 0.06 kcal/min per 1.73 m2). Indirect calorimetry revealed that in cirrhotic patients the percentages of total calories derived from fat (69 +/- 3%), carbohydrate (13 +/- 2%), and protein (17 +/- 4%) were comparable to those found in 36-72-h fasted subjects, but were clearly different from those of overnight fasted normal individuals who derived 40 +/- 6, 39 +/- 4, and 21 +/- 2% from fat, carbohydrate, and protein, respectively. These data are strikingly similar to data obtained through tracer analyses of [14C]palmitate, which showed that in overnight fasted patients with alcoholic cirrhosis, 63 +/- 4% of their total CO2 production was derived from oxidation of 287 +/- 28 mumol free fatty acids (FFA)/min per 1.73 m2. In contrast, normal overnight fasted humans derived 34 +/- 6% of their total CO2 production from the oxidation of 147 +/- 25 mumol FFA/min per 1.73 m2. On the other hand, values obtained from the normal volunteers fasted 36-72 h were similar to the overnight fasted cirrhotic patients. These results show that after an overnight fast the caloric requirements of patients with alcoholic cirrhosis are normal, but the nature of fuels oxidized are similar to normal humans undergoing 2-3 d of total starvation. Thus, patients with alcoholic cirrhosis develop the catabolic state of starvation more rapidly than do normal humans. This disturbed but compensated pattern for maintaining fuel homeostasis may be partly responsible for the cachexia observed in some patients with alcoholic cirrhosis. This study also showed remarkably good agreement between the results obtained with indirect calorimetry and those obtained with 14C tracer analyses.

The disposal of an oral glucose load in patients with non-insulin-dependent diabetes.

Following glucose ingestion, tissue glucose uptake is enhanced and endogenous glucose production is inhibited, thus contributing to the maintenance of normal glucose tolerance. To examine whether these responses are disturbed in diabetes, glucose kinetics after oral glucose administration were studied in 12 non-insulin-dependent diabetic and 10 age- and weight-matched control subjects. A double tracer approach was used, whereby the endogenous glucose pool was labeled with 3-3H-glucose and the oral load with 1-14C-glucose. The two glucose tracers were separated in plasma by a two-step chromatographic procedure, and the two sets of isotopic data were analyzed according to a two-compartment model for the glucose system. Basally, glucose production was slightly higher in diabetics than in controls (2.51 +/- 0.24 v 2.28 +/- 0.11 mg/kg.min, NS) even though the former had higher plasma glucose (189 +/- 19 v 93 +/- 2 mg/dL, P less than .001) and insulin (23 +/- 4 v 12 +/- 1 microU/mL, P less than .05) concentrations. Following the ingestion of 1 g/kg of glucose, oral glucose appeared in the peripheral circulation in similar time-course and amount in the two groups (75 +/- 2% of the load over 3.5 hours in the diabetics v 76 +/- 3% in controls). Endogenous glucose production was promptly inhibited in diabetic and normal subjects alike, but the mean residual hepatic glucose production after glucose ingestion was significantly greater in the diabetic group (17 +/- 2 v 10 +/- 3 g/3.5 h, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol causes acute inhibition of carbohydrate, fat, and protein oxidation and insulin resistance.

To study the mechanism of the diabetogenic action of ethanol, ethanol (0.75 g/kg over 30 min) and then glucose (0.5 g/kg over 5 min) were infused intravenously into six normal males. During the 4-h study, 21.8 +/- 2.1 g of ethanol was metabolized and oxidized to CO2 and H2O. Ethanol decreased total body fat oxidation by 79% and protein oxidation by 39%, and almost completely abolished the 249% rise in carbohydrate (CHO) oxidation seen in controls after glucose infusion. Ethanol decreased the basal rate of glucose appearance (GRa) by 30% and the basal rate of glucose disappearance (GRd) by 38%, potentiated glucose-stimulated insulin release by 54%, and had no effect on glucose tolerance. In hyperinsulinemic-euglycemic clamp studies, ethanol caused a 36% decrease in glucose disposal. We conclude that ethanol was a preferred fuel preventing fat, and to lesser degrees, CHO and protein, from being oxidized. It also caused acute insulin resistance which was compensated for by hypersecretion of insulin.

Acetone Metabolism in Humans During Diabetic Ketoacidosis

Plasma acetone turnover rates were measured with the primed continuous infusion of 2-[14C]acetone in patients with moderate to severe diabetic ketoacidosis. Plasma acetone turnover rates ranged from 1.52 to 15.9 μmol · kg−1 · min−1 (108–1038 n,mol · 1.73 m−2 min−1) and were directly related to the plasma acetone concentrations that ranged from 0.47 to 7.61 mM. The average acetoneturnover rate was 6.45 μmol kg−1 min−1 (533 μmol · 1.73 m−2 min−1), a value twice that obtained in a similar group of diabetic ketoacidotic patients via the single-injection technique of 2-[14C]acetone administration. Degradation of urine glucose revealed that 14C from administered 2-[14C]acetone was principally located in carbons 1, 2, 5, and 6 of the glucose molecule in five of six patients. This distribution is similar to that expected from 2-[14C]pyruvate, suggesting that acetone was converted to glucose through pyruvate. In one patient, label was located predominantly in glucose carbons 3 and 4, indicating that acetone metabolism maybe different in some patients. Acetol (1-hydroxyacetone) and 1,2-propanediol (PPD), two possible metabolites of acetone, were detected in plasma of the patients. The concentrations of Acetol ranged from 0 to 0.48 mM and of PPD ranged from 0 to 0.53 mM. The concentrations of each metabolite were directly related to the plasma acetone concentrations. During the continuous infusion of 2-[14C]acetone, the specific activities of plasma glucose and PPD rose continuously but did not reach constant values. Estimates of theminimal percent plasma glucose and PPD derived from plasma acetone averaged 2.1 and 74%, respectively.

Plasma Acetone Metabolism in the Fasting Human

The metabolism of acetone was studied in lean and obese humans during starvation ketosis. Acetone concentrations in plasma, urine, and breath; and rates of endogenous production, elimination in breath and urine, and in vivo metabolism were determined. There was a direct relationship between plasma acetone turnover (20-77 mumol/m(2) per min) and concentration (0.19-1.68 mM). Breath and urinary excretion of acetone accounted for a 2-30% of the endogenous production rate, and in vivo metabolism accounted for the remainder. Plasma acetone oxidation accounted for congruent with60% of the production rate in 3-d fasted subjects and about 25% of the production rate in 21-d fasted subjects. About 1-2% of the total CO(2) production was derived from plasma acetone oxidation and was not related to the plasma concentration or production rate. Radioactivity from [(14)C]acetone was not detected in plasma free fatty acids, acetoacetate, beta-hydroxybutyrate, or other anionic compounds, but was present in plasma glucose, lipids, and proteins. If glucose synthesis from acetone is possible in humans, this process could account for 11% of the glucose production rate and 59% of the acetone production rate in 21-d fasted subjects. During maximum acetonemia, acetone production from acetoacetate could account for 37% of the anticipated acetoacetate production, which implies that a significant fraction of the latter compound does not undergo immediate terminal oxidation.

Acetone Metabolism During Diabetic Ketoacidosis

The presence and the importance of acetone and its metabolism in diabetic ketoacidosis has largely been ignored. Therefore, we studied acetone metabolism in nine diabetic patients in moderate to severe ketoacidosis. The concentration of acetone in plasma, urine, and breath, and the rates of acetone production and elimination in breath and urine were determined and the rates of vivo metabolism were calculated. Plasma acetone concentrations (1.55–8.91 mM) were directly related and were generally > acetoacetate concentrations (1.16–6.08 mM). The rates of acetone production ranged from 68 to 581 μmol/min/1.73 m2, indicating the heterogeneous nature of the patients studied. The average acetone production rate was 265 μmol/min/1.73 m2 and accounted for about 52% of the estimated acetoacetate production rate. Urinary excretion of acetone remained constant and accounted for about 7% of the acetone production rate in all patients. There was a positive linear relationship between the percentage of the acetone production rate accounted for by excretion in breath and the plasma acetone concentration. At low plasma acetone concentrations, ∼ 20%, and at high plasma acetone concentrations, ∼ 80% of the production rate was accounted for by breath acetone. In contrast, there was a negative linear relationship between the percentage of acetone production rate undergoing in vivo metabolism and plasma acetone concentration. At low plasma acetone concentrations, ∼ 75%, and at high concentrations, ∼ 20% of acetone production rate was accounted for by in vivo metabolism. Radioactivity from 2-[14C]-acetone was variably present in plasma acetone, glucose, lipids and proteins. No radioactivity was found in plasma acetoacetate, beta-hydroxy butyrate or free fatty acids or other anionic compounds. Exchange rates of acetone into other metabolites could not be estimated because of non-steady-state precursor product relationships in these patients.

Ketone-body production and oxidation in fasting obese humans.

Rates of plasma acetoacetate and total ketone-body production and oxidation to CO2 were determined by an isotope tracer technique in eight obese subjects undergoing progressive starvation. After a brief fast and under conditions of mild ketonemia and minimal ketonuria, rates of acetoacetate and total ketone-body production and oxidation were directly related to the increasing plasma concentration. After a longer fast and with severer ketonemia, acetoacetate and total ketone-body production and oxidation rates were higher but became constant and unrelated to the plasma concentrations. The maximum rates of total ketone-body production and oxidation were about 150 g/24 h and 129 g/24 h, respectively. Although an increased ketone-body production was the primary factor responsible for the hyperketonemia, an imbalance between production and removal of the ketone bodies cannot be excluded. Such an imbalance could account, at least in part, for the developing hyperketonemia and for the lack of relationship between production rates and plasma concentrations.

Energy metabolism in feasting and fasting.

During feasting on a balanced carbohydrate, fat, and protein meal resting metabolic rate, body temperature and respiratory quotient all increase. The dietary components are utilized to replenish and augment glycogen and fat stores in the body. Excessive carbohydrate is also converted to lipid in the liver and stored along with the excessive lipids of dietary origin as triglycerides in adipose tissue, the major fuel storage depot. Amino acids in excess of those needed for protein synthesis are preferentially catabolized over glucose and fat for energy production. This occurs because there are no significant storage sites for amino acids or proteins, and the accumulation of nitrogenous compounds is ill tolerated. During fasting, adipose tissue, muscle, liver, and kidneys work in concert to supply, to convert, and to conserve fuels for the body. During the brief postabsorptive period, blood fuel homeostasis is maintained primarily by hepatic glycogenolysis and adipose tissue lipolysis. As fasting progresses, muscle proteolysis supplies glycogenic amino acids for heightened hepatic gluconeogenesis for a short period of time. After about three days of starvation, the metabolic profile is set to conserve protein and to supply greater quantities of alternate fuels. In particular, free fatty acids and ketone bodies are utilized to maintain energy needs. The ability of the kidney to conserve ketone bodies prevents the loss of large quantities of these valuable fuels in the urine. This delicate interplay among liver, muscle, kidney, and adipose tissue maintains blood fuel homeostasis and allows humans to survive caloric deprivation for extended periods.

6Ketosis of starvation: A revisit and new perspectives

During starvation ketone bodies, acetoacetate (AcAc), 3-hydroxybntyrate (fl-OHB) and acetone accumulate in the body fluids. AcAc and /3-OHB are synthesized in the liver primarily from the partial oxidation of long-chain fatty acids. They are released into the blood as short-chain fatty acids, dissociate to become water-soluble anions and are distributed at different concentrations in the water components of the body (Owen et al, 1973). Acetone is probably formed by spontaneous decarboxylation of AcAc. Acetone is a neutral compound, and, unlike AcAc and/3-OHB, it does not affect blood bicarbonate concentration, arterial blood gases or pH (Sulway and Malins, 1970). Acetone is soluble in both water and lipids, and therefore it is distributed throughout the body (Reichard et al, 1979). During food deprivation, starvation ketosis is arbitrarily defined as being present when the minimum blood/plasma concentration of AcAc is about 1.0 mmol/1. Concurrent concentrations of/3-OHB and acetone are usually about 2.0 and 0.5 mmol/1, respectively. Such values are usually present after 2- 3 days of total starvation. Maximal blood/plasma concentrations of AcAc (2- 4 mmol/1),/3-OHB (5 - 12 retool/l) and acetone (3 -5 mmol/l) develop after several weeks of total fasting. The arbitrary definition of starvation ketosis is centred on the plasma/serum AcAc concentration, because the only semiquantitative test preparations, widely available to detect the presence of ketone bodies in biological fluids, depend upon the reagent nitroprusside to react with AcAc. Contrary to popula~ opinion, the presence of acetone or/3-OHB does not augment nitroprusside reactivity with AcAc. Plasma/serum/urine concentrations of AcAc below 0.5 mmol/1 are nonreactive with commercially available diagnostic tests. However, these semiquantitative tests develop reactions that are roughly concentration dependent. Nitroprusside tests show 1 + (trace to small) reactivity with 1 -2 mmol AcAc, 2 + (small to moderate) reactivity with 3 -4 mmol AcAc and 3 + (moderate to large) reactivity with 5 - 10 mmol AcAc. Thus, high

Comparative measurements of glucose, beta-hydroxybutyrate, acetoacetate, and insulin in blood and cerebrospinal fluid during starvation.

Abstract The possibility that altered central nervous system (CNS) metabolism is reflected by changes in the constituents of the cerebrospinal fluid (CSF) was investigated. From eight obese subjects undergoing total starvation for weight reduction, overnight and 21-day fasting specimens of venous blood and lumbar CSF were obtained nearly simultaneously to determine the concentrations of glucose, beta-hydroxybutyrate (β-OHB), acetoacetate (AcAc), and immunoreactive insulin (IRI). After 21 days of starvation, the glucose concentration fell in both blood and CSF. The decrease in blood glucose was greater than the decline in CSF glucose, resulting in a diminished blood-CSF difference. Concentrations of β-OHB and AcAc in blood and CSF were elevated after prolonged fasting, but blood levels exceeded those in CSF, producing an increased blood-CSF ketone body difference. After an overnight and 21-day fast, the IRI levels in CSF were about one-half of the serum levels. These data suggest that metabolic alterations in CNS metabolism during prolonged starvation are reflected in substrate concentrations observed in CSF, and demonstrate that insulin is presented in the CSF of man.