Frank Rees Smith

The effects of diseases of the liver, thyroid, and kidneys on the transport of vitamin A in human plasma.

The effects of diseases of the liver, the thyroid, and the kidneys on the retinol-binding protein (RBP)-prealbumin (PA) system responsible for the transport of vitamin A in plasma were examined, using a radial gel diffusion immunoassay for PA and the previously described radioimmunoassay for RBP. Measurements were made on plasma samples from 118 normal subjects, 31 patients with cirrhosis, 5 with chronic active hepatitis, 27 with acute viral hepatitis, 14 patients with hyperthyroidism, 7 with hypothyroidism, and 26 patients with chronic renal disease of varying etiologies. In the patients with liver disease, the levels of vitamin A, RBP, and PA were all markedly decreased and were highly significantly correlated over a wide range of concentrations. Serial samples were available in 19 patients with acute hepatitis; as the disease improved the plasma concentrations of vitamin A, RBP, and PA all increased. In patients with acute hepatitis RBP concentrations correlated negatively with the levels of plasma bilirubin, glutamic-oxaloacetic transaminase, and alkaline phosphatase. In the hyperthyroid patients both RBP and PA concentrations were significantly lower than normal; in hypothyroidism, neither protein showed levels significantly different from normal. In both hyper- and hypothyroidism and in liver disease, the molar ratios of RBP:PA and of RBP:vitamin A were not significantly different from normal.Patients with chronic renal disease had marked abnormalities in the plasma concentrations of RBP and vitamin A and in the molar ratios examined. In renal disease the levels of both RBP and vitamin A were greatly elevated, while the PA levels remained normal. The molar ratios of RBP:PA and of RBP:vitamin A were both markedly elevated. In many patients RBP was present in molar excess as compared with PA. The presence of a relatively large proportion of free RBP, not complexed to PA, in some patients with chronic renal disease was confirmed by gel filtration. The free RBP, present in molar excess, was capable of forming a complex with additional purified PA added to the plasma. The kidneys appear to play an important role in the normal metabolism of RBP.

Vitamin A Transport in Human Vitamin A Toxicity

The plasma retinol transport system was studied in three patients with chronic hypervitaminosis A. The toxic state in each was associated with increased plasma concentrations of total vitamin A, and particularly of retinyl esters. The concentrations of plasma retinol-binding protein and prealbumin were, in contrast, non to retinol-binding protein. These limited clinical data support conclusions from detailed studies with hypervitaminotic rats, which suggest that vitamin A toxicity occurs when excessive amounts of vitamin A are presented to cell membranes in association with plasma lipoproteins, rather than specifically bound to retinol-binding protein. Retinol-binding protein may not only regulate the supply of retinol to tissues but also protect tissues from the surface-active properties of the vitamin.

Effects of lipoproteins on plasma viscosity

Patients with hypertriglyceridemia and mixed hyperlipidemia have been found to have mean plasma viscosities significantly higher than controls (P less than 0.005). In a group of 70 hyperlipidemic patients and controls, plasma viscosity was correlated with plasma triglyceride concentration (r = 0.56, P less than 0.01) and to a lesser extent with the concentration of plasma cholesterol (r = 0.29, P less than 0.05). When isolated lipoprotein fractions were added to lipoprotein-free plasma in increasing concentration over a physiological range, a highly significant linear relationship between plasma viscosity and chylomicron concentrations (r = 0.98, P less than 0.001) was apparent. Furthermore, when chylomicrons were removed by ultracentrifugation, viscosity returned to baseline levels. Added VLDL produced a lesser effect (r = 0.70, P less than 0.001) and added LDL, over the range of cholesterol concentration studied, had no influence on viscosity. These studies indicate that chylomicrons in particular can increase plasma viscosity. Viscosity increases of the magnitude demonstrated may in turn alter blood flow and thus contribute to symptoms such as intermittent claudication. Chylomicron-induced increases in plasma viscosity and subsequent decreases in local pancreatic blood flow may be one of the factors involved in the known relationship between severe chylomicronemia and acute pancreatitis.

Defects of taste and smell in patients with hypothyroidism

Taste and smell functions were measured in 18 unselected patients with untreated primary hypothyroidism, and in 15 of the 18 patients after treatment with thyroid hormones. Before treatment, 9 of the 18 patients (50 per cent) were aware of some alteration in their sense of taste, and 7 of the 18 patients (39 per cent) were aware of some alteration in their sense of smell. Distoritions of tase (dysgeusia) and smell (dysosmia) were frequent complaints among the untreated patients; dysgeusia was observed by 7 patients (39 per cent) and dysosmia by 3 patients (17 per cent). Median detection and recognition thresholds for four taste stimuli salt (sodium chloride), sweet (sucrose), sour (hydrochloric acid) and bitter (urea), and for two smell stimuli (pyridine and nitrobenzene), were determined in each patient before and after treatment with thyroid hormones. Before treatment, decreased taste acuity (hypogeusia) for at least one stimulus was observed in 14 of the patients (83 per cent); the most common abnormalities were in the detection and recognition of bitter stimuli. Median detection thresholds for both smell stimuli were also markedly elevated (hyposmia) before therapy. Treatment with throid hormones largely reversed both the taste and smell defects. In one patient, taste and smell abnormalities were completely corrected after 16 days of treatment with thyroxine. This study indicates that taste and smell defects are common clinical abnormalities in primary hypothyroidism, and suggests that these defects may contribute to the anorexia and lack of interest in eating which are frequently observed.

HYPOSMIA IN ACUTE VIRAL HEPATITIS

Abstract 19 patients with acute viral hepatitis have been found to have decreased olfactory acuity (hyposmia) which is associated with dysosmia and dysgeusia. Olfactory acuity was measured with three vapours—pyridine in water and nitrobenzene and thiophene in mineral oil. Hyposmia, called type-II hyposmia, lessened as the illness subsided. Improvement in olfactory acuity was inversely related to the plasma-bilirubin and directly related to the plasma-retinol-binding-protein level. Abnormalities of olfaction and taste may be major factors in the anorexia of hepatitis. Measurement of olfactory acuity is a rapid, simple means of assessing and monitoring hepatic function.

Vitamin-A reversal of abnormal dark adaptation in cirrhosis. Study of effects on the plasma retinol transport system.

Of 26 patients hospitalized with mild to moderate alcohol-associated cirrhosis, 14 had dark-adaptation abnormalities consistent with marginal vitamin-A status. The response of dark adaptation and the plasma retinol transport proteins, retinol-binding protein and prealbumin, was studied in 12 of these patients after daily oral vitamin-A supplements of 3300 microgram. Vitamin-A supplementation was associated with significant (p less than 0.05-0.005) improvement in dark adaptation and increased plasma concentrations of retinyl esters, retinol, and retinol-binding protein. Thus in patients with cirrhosis and marginal vitamin-A status, supplemental vitamin-A therapy appears to stimulate retinol-binding protein release from the liver. This enhancement of plasma retinol transport and delivery of retinol to peripheral tissues such as the retina is one of several factors that may serve to optimize vitamin-A nutritional status in patients with cirrhosis.

Radioimmunoassay of human plasma retinol-binding protein

A radioimmunoassay for human plasma retinol-binding protein (RBP) has been developed utilizing a double antibody precipitation technique. RBP was purified 1500- to 2000-fold by procedures described previously. A specific anti-human RBP antiserum was prepared in rabbits by three once-weekly injections of purified RBP emulsified with Freunds adjuvant. RBP was iodinated with (131)I and the RBP-(131)I was purified by gel filtration on Sephadex G-100 after complex formation with human plasma prealbumin. The RBP-(131)I was completely (> 95%) immunoprecipitable in the presence of an excess of specific antiserum, it was not (< 5%) immunoprecipitable in the absence of specific antiserum, and it could be completely displaced from antibody by excess unlabeled RBP. The standard curve obtained in the immunoassay with normal plasma was identical to that with pure RBP. Duplicate samples differed from their mean by 5 +/-5% (+/-SD). There was a quantitative recovery of pure RBP added in varying amounts to normal plasma. The immunoassay accurately measured RBP in amounts of 10-100 ng per assay tube. There was no significant difference in the immunoreactivity of apo-RBP as compared to holo-RBP. The mean plasma values (+/-SEM) for a group of 76 normal subjects were 47.2 +/-1.6 mug/ml for males and 41.6 +/-1.6 mug/ml for females. Plasma RBP levels were markedly depressed (15 +/-2.3 mug/ml) in 14 patients with acute viral hepatitis. There was a highly significant correlation between the plasma levels of RBP and of vitamin A in both normal subjects and patients with hepatitis. In all subjects plasma RBP was generally saturated with retinol. The data suggest that under normal circumstances RBP circulates almost exclusively as the holoprotein.

Parameters of the three-pool model of the turnover of plasma cholesterol in normal and hyperlipidemic humans.

Long-term studies (32-49 wk) of the turnover of plasma cholesterol were conducted in 24 subjects. Eight subjects were normilipidemic, six had hypercholesterolemia, eight had hypercholesterolemia and hypertriglyceridemia, and two had hypertriglyceridemia alone. 10 of the hyperlipidemic patients had a definite familial disorder. In all subjects (except one for whom complete data were not available), the same three-pool model previously described gave the best fit for the data. The parameters of the three-pool model observed in the normal subjects were compared with the model parameters found in the patients with the different kinds of hyperlipidemia. In addition, single and multiple regression analyses were conducted to explore the relationships between the model parameters and various physiological variables, including age, body size, and serum lipid concentrations. Using this approach, significant differences between groups, or correlations with serum lipid levels were seen for several parameters of the three-pool model: the production rate (PR); the size of the rapidly exchanging pool 1 (M1); all estimates of the size of the most slowly equilibrating pool 3 (M3); and the rate constant k21. The PR in normal subjects (1.14 +/- 0.19 g/day, mean +/- SD) was not significantly different from that found in patients with hypercholesterolemia, with or without hypertriglyceridemia. The major determinant of cholesterol PR was overall body size, expressed either as total body weight or as surface area. The correlations between PR and indices of adiposity (percent ideal weight and excess weight), although statistically significant, were much weaker in this nonobese population. After adjustment for body size variation, cholesterol PR was not correlated with the serum cholesterol concentration but was probably (P less than 0.05) correlated with the triglyceride concentration. When the two patients with very high triglyceride concentrations were excluded, however, no correlation was observed between adjusted PR and triglyceride level. It is probable that hypertriglyceridemic patients represent a heterogeneous population, in which the majority do not show increased cholesterol PR. M1 was correlated with all body size variables, but most strongly with excess weight. After adjusting for the effects of body size, M1 was also correlated and triglyceride. Major differences were found in the relationships between the physiological variables and the sizes of pools 2 and 3. M2 was correlated neither with any of the indices of body size or adiposity, nor with the serum levels of either cholesterol or triglyceride. In contrast, all estimates of M3 were correlated with indices of adiposity (but not of overall body size) and with the serum cholesterol concentration. Thus, the amount of cholesterol in slowly equilibrating tissue sites appears to particularly increase with elevations of the serum cholesterol level. The results also confirm previous data that adipose tissue cholesterol is an important part of pool 3.

Zinc and copper metabolism in acute viral hepatitis.

Patients with acute viral hepatitis were found to have decreased serum concentrations of total zinc, increased serum concentrations of diffusible zinc, and increased urinary zinc excretion. As the illness subsided serum concentrations of total zinc rose to normal, serum concentrations of diffusible zinc fell to normal, and urinary zinc excretion decreased. Total serum zinc concentration was related inversely to serum diffusible zinc and directly to plasma levels of retinol-binding protein (RBP) and total protein. Serum diffusible zinc was inversely related to plasma RBP and total protein and directly to plasma bilirubin and serum copper. The changes in serum and urinary zinc may be related to changes in the manner by which zinc is bound to serum proteins, particularly albumin. Total serum copper concentrations were normal in the early, acute phase of this clisease but increased to greater than normal levels as the illness subsided. This increase was accounted for entirely by increases in the concentration of ceruloplasmin copper.

Disordered Gustatory Acuity in Liver Disease

Disordered gustatory acuity was demonstrated in 22 patients with acute viral hepatitis and in 16 patients with chronic liver disease utilizing subjective responses and objective measurements of detection and recognition thresholds and scaling for NaCl, sucrose, HCl, and urea. In patients with early hepatitis and those with chronic liver disease, the magnitude and the uniformity of the threshold elevations were comparable, implying that disordered gustatory acuity reflects disordered hepatic function per se. Patients with acute hepatitis showed a significant fall in taste thresholds (improvement in acuity) as the hepatitis waned, indicating that the gustatory defect is reversible. This disorder of gustatory acuity may contribute to the anorexia commonly found in patients with liver disease.