Protein turnover in advanced lung cancer patients

Protein

Turnover

in Advanced

Lung Cancer

Patients

Ernest W. Richards, Calvin L. Long, Karl M. Nelson, Ocilia K. Tohver, John A. Pinkston, Rudolph M. Navari, and William S. Blakemore Understanding the extent to which changes in whole-body protein kinetics contribute to the commonly observed weight loss and decrease in lean body mass (LBM) in patients with cancer is currently obscured by conflicting reports in the literature. While several studies have reported significant increases in whole-body protein turnover (WBPT), synthesis (WBPS), and catabolism (WBPC) in patients with cancer, others have failed to confirm these observations. We have measured whole-body protein kinetics using a primed constant infusion of 15N-glycine in a homogenous group of 32 newly diagnosed advanced lung cancer patients with comparable staging and before any antineoplastic treatment, and in 19 normal healthy volunteer controls. Urinary urea and ammonia 1sN enrichment was determined in individually collected urine samples obtained during the 24-hour study period and averaged for the determination of protein kinetics. During the last 6 hours of urine collection, samples were obtained hourly for determination of 15N plateau enrichment. Twenty-four-hour urinary nitrogen and creatinine excretion was determined from 24-hour pooled urine samples. Resting metabolic expenditure (TIME) was determined by indirect calorimetry and LBM was estimated from deuterium oxide dilution. Age, body weight, LBM, RME, and 24-hour urinary nitrogen excretion did not differ between cancer and control subjects. WBPT, WBPC, and WBPS (g/kg/d) were significantly increased in lung cancer patients. However, when the same results were expressed either per kilogram LBM or per gram 24-hour urinary creatinine excretion, WBPT, WBPC, and WBPS rates were not statistically different from those of the controls. Net protein synthesis (WBPS - WBPT) was not different from that of the controls, regardless of how data were expressed. These results reveal that protein kinetics in the lung cancer patients were not significantly different from those of the control group when normalized to active muscle mass, and suggest that newly diagnosed noncachectic advanced lung cancer patients do not exhibit a significant increase in whole-body protein kinetic rates. Copyright 6 1993 by W.B. Saunders Company

L

OSS OF LEAN BODY TISSUE occurs with the progression of most neoplastic diseases. This weight loss often progresses to clinically significant wasting, culminating in cancer cachexia.‘-4 Cancer cachexia is described by Theologides5 as a syndrome characterized by anorexia, early satiety, anemia, and marked asthenia in addition to weight loss, and has been reported to be almost universal in patients with advanced malignancies6 These responses in the cancer patient constitute a complex metabolic abnormality and are not simply a result of starvation. Although it is generally agreed that decreased nutrient intake plays an important role in the progressive weight loss and wasting of lean body mass (LBM) associated with cancer cachexia, there still remains some controversy as to the contributory role of alterations in substrate metabolism. It is clear that anorexia and decreased nutrient intake cannot fully account for the weight loss commonly observed in patients with malignant neoplasms7 The inability of dietary intake to meet the metabolic demands of patients with cancer must be manifested in the combined effects of diminished nutrient intake and aberrations in whole-body energy and protein metabolism. There are several studies that have addressed the contributory role of alterations in energy and substrate metabolism; however, results have been conflicting. In addition, studies addressing the dynamics of protein metabolism in homogenous groups of patients with cancer either on a whole-body basis or in individual tissues are limited and often demonstrate conflicting results. Increased rates of whole-body protein turnover (WBPT), synthesis (WBPS), and catabolism (WBPC) have been previously reported in patients with colorectal cancer* or non-oat-cell lung cancer,g-t* and several groups of patients with mixed cancer types.t2-t4 However, there are also studies that report no change in protein kinetics in patients with gastrointestinal Metabolism,Vol42,

No 3 (March), 1993: pp 291-296

cancer, I5 colorectal cancer,r6 lung cancer,” and esophageal cancer.18 These conflicting reports may be the result of such factors as small samples of patients with cancer, utilization of antineoplastic treatment modalities before metabolic study periods, heterogenous nature of the patients sampled with regard to cancer type and stage, differences in the degree of cancer cachexia and weight loss, and variable samples of subjects without cancer to serve as controls. With regard to protein kinetics in patients with advanced lung cancer, Heber et al9 reported increased WBPT using r4C-lysine and increased 3-methylhistidine excretion in 12 postabsorptive patients with non-small-cell lung cancer. Similarly, Melville et aI*’ reported increased protein turnover using *3C-leucine in a group of nine newly diagnosed postabsorptive lung cancer patients before they had undergone any treatment. Conversely, Emery et alI7 observed decreased synthesis and breakdown of protein in muscle, and normal WBPS and WBPC rates in a group of four lung cancer patients in the fed state. In an attempt to further measure the extent and direction of alterations in protein kinetics in patients with advanced lung cancer, r5N-glycine metabolism was evaluated in a homogenous group of 32 stage III and IV advanced lung cancer patients immediately after diagnosis and before any antineoplastic treatment. WBPT, WBPC, and WBPS rates were determined and compared with those of a group of 19 From the Department of Research, The Baptist Medical Centers, Birmingham, AL. Submitted October 15, 1991; accepted May 14, 1992. Supported by National Institutes of Health Grant No. CA-42972. Address reprint requests to Calvin L. Long, PhD, Baptist Medical Centers, Department of Research, 701 Princeton Ave, Birmingham, AL 35211. Copyright 0 I993 by W.B. Saunders Company 0026-0495/93/4203-0004$03.00/0 291

RICHARDS ET AL

292

normal healthy controls without significant weight loss. Protein kinetic data are expressed per kilogram total body weight and per kilogram LBM or per gram 24-hour urinary creatinine excretion to account for potential differences in active muscle mass.

Table 1. Clinical Diagnosis and Cancer Staging of

Lung Cancer

Patients

Patient NO.

stage

TNM’

Small cell

IV

T3 N2 Ml

Small cell

Ill

T3 NO Ml

M

Small cell

Ill

Tl NO Ml

M

Small cell

IV

TX NO Ml

Small cell

Ill

T4 N2 MO

Adenocarcinoma

Ill

T2 Nl MO

SF2

Diagnosis

1

F

2

F

3

Materials

4 5

M

The isotope infused was t5N-glycine (99 atom percent excess [APE]; MSD Isotopes, Montreal, Quebec, Canada). Solutions of t5N-glycine were prepared in sterile 0.45% NaCl and passed through 0.22~urn filters into sterile, pyrogen-free vials; the solutions were confirmed to be sterile and nonpyrogenic by an independent testing laboratory. For each infusion, an aliquot of the infusate was analyzed for the precise isotope concentration to calculate the actual infusion rate for each patient.

6

M

7

M

Adenocarcinoma

III

T2 NO MO

6

F

Adenocarcinoma

IV

T3 N2 Ml

MATERIALS

AND METHODS

Subjects

9

F

Adenocarcinoma

IV

T2 N3 Ml

10

M

Adenocarcinoma

Ill

T2 N3 MO

11

M

Large cell

IV

T3 N2 Ml

12

F

Large cell

IV

T4 NO Ml

13

M

Large cell

Ill

TX NX MX

14

M

Squamous cell

III

T3 NO MO

15

M

Squamous cell

IV

Tl Nl Ml

16

M

Squamous cell

IV

T2 Nl Ml

Patients with advanced lung cancer were recruited from the cancer centers of the Baptist Medical Centers on diagnosis and before undergoing any antineoplastic treatment. Ah cancer patients were ambulatory and free of any other metabolic or nutritional disease. The lung cancer group consisted of 32 patients (nine women and 23 men) with a mean age of 58.4 * 1.1 years (age range, 48 to 77 years). Table 1 presents the clinical diagnosis, stage, and TNM classification for each lung cancer patient; tumor type was assessed by histological examination of tumor biopsy samples. Sixteen patients presented with evidence of distant metastasis (Ml), while the remaitting patients presented with either extensive primary tumor (T3, T4) or regional lymph node involvement (Nl, N2, N3). All patients were diagnosed with either stage III or IV lung cancer. The control group consisted of 19 normal healthy volunteer subjects admitted to our clinical research unit for the 24-hour study period. All controls were ambulatory and free of any known metabolic or nutritional disease, and had the same general smoking habits as the lung cancer patients as assessed by smoking history and pulmonary function tests. The Institutional Review Board of the Baptist Medical Centers approved the experimental protocol. Before their participation, the nature, purpose, and risks of the study were explained in detail to all patients and written informed consent was obtained.

for later analysis of the APE 15N enrichment isotope ratio mass spectrometer.

Protein Kinetics

Analysis of Samples

All patients were admitted to our clinical research unit at 12:00 and were fasted throughout the entire 24-hour study period. WBPT was determined using a primed constant infusion of i5N-glycine as originally described by Picou and Taylor-Robertsi and later modified by Jeevanandam et aLi At the start of the 24-hour study period, patients received a priming bolus dose of sterile, pyrogen-free 2.25 mg 15N-glycine/kg body weight, followed by a continuous infusion of 0.00125 mg t5N-glycine/kg body weight/min delivered in a 0.9% normal saline solution. The continuous infusion was delivered using a volumetric infusion pump (IMED, Imed Corporation, San Diego, CA) at a rate of 75 mL/h for the 24-hour study period. Urine samples were collected each time the patient voided during the first 18 hours and then hourly for the remainder of the 24-hour study period to provide an accurate reflection of steady-state i5N-urea and 15N-ammonia enrichment, as demonstrated in the representative curves of Fig 1. Aliquots of each urine sample (10%) were then pooled and used for the determination of 24-hour nitrogen and creatinine excretion rates. Individual urine samples were frozen in dry ice and stored

For the determination of i5N isotopic enrichment, urea and ammonia were separated from each individual urine sample using a Conway diffusion dish. Four milliliters urine were pipetted into the outer well of a Conway diffusion dish; the center well contained 3.0 mL 1% HzSO+ Two milliliters of a saturated KzCOs solution was then added to the urine, and the Conway dish was covered and allowed to sit at room temperature overnight. Liberated ammonia was trapped in the 1% H2S04 solution. The urea (outer well) and (NH&S04 (inner well) solutions were frozen for later isotopic mass spectral analysis. Approximately 3.0 mL of the K&03-treated ammonia-free urine samples was treated with 1.5 mL aged hypobromite and 1.0 mL 0.1% KI solution in separate legs of an evacuated Rittenberg tube to liberate the nitrogen gas for mass analysis.20~2i The same preparative procedures were also used for the analysis of t5N enrichment of the (NH&S04 samples. The glycine concentration of the primed and constant infusion was measured using a Beckman automatic amino acid analyzer (Beckman Instruments, Palo Alto, CA). The i5N:i4N isotope ratios were determined in duplicate on each

PM

17

M

Squamous cell

Ill

T3 Nl MO

18

M

Squamous cell

Ill

T3 NO MO

19

M

Squamous cell

Ill

T2 NO MO

20

M

Squamous cell

Ill

TXNXMl

21

M

Squamous cell

Ill

T4 NO MO

22

F

Squamous cell

IV

T2 NX Ml

23

M

Squamous cell

IV

Tl NO MX

24

M

Squamous cell

III

T2 N3 MO

25

M

Squamous cell

Ill

TX NX MX

26

F

Squamous cell

Ill

T3 N2 MO

27

F

Squamous cell

IV

TX NX Ml

28

M

Squamous cell

Ill

T2 N3 MO

29

M

Squamous cell

Ill

T3 NO MO

30

M

Squamous cell

IV

T3 N3 Ml

31

F

Undiff NSCLC

IV

T4NOMl

32

M

Undiff NSCLC

Ill

T3 Nl Ml

Abbreviation:

Undiff NSCLC, undifferentiated

non-small-cell

lung

cancer. *Tumor, node, metastasis staging of lung cancer.

using a Nier-type

PROTEIN TURNOVER IN ADVANCED

LUNG CANCER

293

aliquot from each individual urine sample collected during the 24-hour study period. After standard microKjeldahl digestion at 450°C for 1 hour, urinary nitrogen content was measured in an automated Encore clinical chemistry analyzer (Baker Instruments. Allentown, PA). Twenty-four-hour urinary creatinine excretion was measured using the Jaffee reaction and the Encore analyzer system.

Nutritional Status

0.15

-

0.10

-

Nutritional status was assessed at the beginning of the study using standard anthropometric and biochemical parameters. Body composition was evaluated using the technique of deuterium oxide dilution. LBM was estimated from total body water values determined from deuterium nuclear magnetic spectroscopic measurements of deuterium oxide dilution.‘3.” Fat mass was then determined as the difference between body weight and LBM. Visceral protein status was assessed using plasma albumin levels and total lymphocyte count as determined from complete blood counts with differential. In addition, assessment of biochemical and hematological parameters included blood urea nitrogen (BUN), electrolytes. lipids, hemoglobin. and hematocrit.

Indirect Calorimetry I-

O

5

20

25

Fig 1. 15N APE of ammonia and urea obtained from urine samples collected hourly during the prime-constant infusion of ‘SN-glycine in control and cancer patients. The average l&NAPE is also presented.

sample using a 60” mass spectrometer with a precision of approximately 2 parts in 100,000. The stability of the instrument and activity of the hypobromite and 0.1% KI solution were checked periodically during the analysis. Residual correction and corrections for air contamination using mass 32 peak heights were routinely applied to individual samples, and all values were normalized with respect to a standard nitrogen gas that was analyzed between every three to four sample runs. For all samples. the APE was obtained by subtracting the atom percent of samples obtained before the ‘sN prime and infusion from each sample. The calculation of whole-body protein kinetics was made using the stochlastic model as described by Picou and Taylor-Roberts.‘” It was assumed that under steady-state conditions and at isotopic equilibrium the proportion of the isotope excreted in an end product of nitrogen metabolism (as urea or ammonia) was the same as the proportion of the flux excreted in the same end product. Since steady-state plateau values of APE in urea and ammonia are not the same and their relative contributions to the calculation of WBPT are not yet clearly established, they were given equal weighting.“,rb,z” The flux or nitrogen turnover rate Q (mg Nikgimin) is defined as the flow of nitrogen into and out of the metabolic nitrogen pool under steady-state conditions, and was calculated by dividing the isotope infusion rate I (mg 15N/kg/min) by the average plateau iSN APE from the urinary end products (urea and ammonia), ie, Q = 100 x (I/APE). Since the patients were fasted overnight and were without any nitrogen or energy intake during the 24-hour study period, fux or Q is equal to the catabolic rate C. The synthesis rate S equals Q minus the urinary nitrogen excretion E,, as demonstrated in the following equation: Q = (C + Nlntake) = (S + E,). Urinary nitrogen level and creatinine excretion were determined

from pooled 24-hour urine samples constructed by taking a 10%

The resting metabolic expenditure (RME) of each subject was measured at 8:30 AM following a 24-hour fast by indirect calorimetry with a ventilated-hood system.“5.‘h Expired gases were continuously monitored for CO2 and 02 content for three 20.minute periods over 3 hours. The measurements were averaged and extrapolated to a 24-hour volume of CO2 production and 02 consumption. The caloric equivalent of 0: consumed was determined from the nonprotein respiratory quotient and Lusk’s table.?7

and was expressed LBM/d).

as the RME (kcal/d;

kcallkgid;

kcalikg

Data Analysis Initial statistical evaluation of differences between individual histological types of lung cancer was performed using ANOVA and revealed no significant difference between the various types of stage III and IV lung cancer patients. Significant differences between lung cancer patients and controls were therefore determined using the unpaired Student’s t test as described by Snedecor and Cochran2s Differences between groups were considered statistically significant if P was less than .05; all values are reported as the mean ? SEM. RESULTS

Table 2 presents the nutritional characteristics of lung cancer patients and controls. Patients with cancer did not differ from control subjects with respect to age, height, body weight, ideal body weight, LBM, body mass index, or hematocrit. The white blood cell count and total lymphocyte count were within normal clinical ranges for both groups and therefore did not suggest any significant nutritional deficiency or compromise in immune status. In addition, biochemical and hematological analyses of hemoglobin, hematocrit, plasma glucose, plasma total ketones. plasma electrolytes (Na, K, Cl, CO& and BUN were comparable between cancer patients and controls during the study period. The increased stated weight loss (8.1% * 1.2%) and depressed plasma albumin levels of 3.2 g/dL in the lung cancer group were the only nutritional

294

RICHARDS ET AL

Table 2. Nutritional Characteristics of Lung Cancer Patients and Controls CalVXN

Parameter Age

W

Height (cm)

Control P Value’

Patients

Subjects

58.4 + 1.1

57.4 + 1.2

,568

172.5 & 1.7

169.5 + 2.4

,304

Weight (kg)

65.7 * 2.2

60.6 + 3.7

,208

IBW (kg)

65.3 + 1.2

63.1 2 1.8

,304 ,497

LBM (kg)

48.9 r 1.6

47.0 + 2.4

BMI (kg/m*)

22.0 + 0.6

20.8 t 0.8

,204

Hematocrit (%)

39.2 2 1.0

41.2?

,184

1.2

Stated weight loss (%)

8.1 + 1.2

2.6 ? 1.5

,008

Albumin (g/dL)

3.2 2 0.1

3.9 * 0.1

< ,001

Abbreviations: determined

IBW, ideal body weight

from deuterium

based on height; LBM,

oxide dilution; BMI, body mass index

urinary creatinine excretion basis (g/g creatinine/d) to facilitate a comparison of whole-body protein kinetics with regard to the potential for changes in body composition in patients with advanced cancer. When whole-body protein kinetics were expressed on a body weight basis, significant increases in WBPT and WBPS were observed in advanced cancer patients as compared with normal healthy controls. However, when these data were normalized to skeletal muscle mass as reflected by both LBM and 24-hour urinary creatinine excretion, WBPT and WBPS were no longer significantly different from the control values. Net protein synthesis was not significantly different between the two groups, regardless of whether it was expressed on a body weight, LBM, or 24-hour urinary creatinine excretion basis.

(wt/ ht2).

DISCUSSION

*Unpaired Student’s t test for cancer patients v controls.

parameters that were perhaps suggestive of the onset of cancer cachexia. The RME of the cancer patient group was not statistically different from that of the controls (1,670 * 54 v 1,536 ? 78 kcal/d, respectively; P = .151). In addition, when expressed on either a total body weight or LBM basis, there was still no difference between patients with advanced lung cancer and controls. Mean urinary nitrogen losses also were not significantly different between cancer patients and controls (133.4 + 8.1 v 139.7 + 9.0 mg/kg/d, respectively; P = .621). In addition, mean 24-hour urinary creatinine excretion in the cancer group versus the controls was not statistically different (1.2 f 0.1 v 1.1 2 0.1 g/d, respectively; P = .269). When further analyzed with regard to sex, 24-hour urinary creatinine excretion in male cancer patients and controls was 19.2 + 0.6 and 18.3 ? 1.4 mg/kg/d, respectively (P = SO3). For female cancer patients and controls, creatinine excretion was 15.3 ? 1.9 and 16.9 * 0.7 mg/kg/d, respectively (P = .431). Together, these data demonstrate that both cancer patients and their controls were very similar with regard to muscle mass and body composition. The attainment of lSN isotopic steady state in both cancer patients and controls is demonstrated in the representative plot of Fig 1. Using a primed constant infusion, isotopic steady state was achieved within 15 + 2 hours for both urinary end products, urea and ammonia. Since estimates of whole-body protein kinetics are best described by using the mean of urea and ammonia enrichment values,l3J6,22 the end product arithmetic average values were used to calculate WBPT, WBPS, and WBPC rates. Although the absolute values of WBPT, WBPS, and WBPC may change depending on which end product is used in their calculation, the conclusions drawn when comparing changes in protein kinetics between two groups are consistent. Results of whole-body protein kinetic studies for advanced lung cancer patients and their controls are presented in Table 3. WBPT is equal to WBPC under our study conditions, since all patients were without any nutrient intake throughout the 24-hour study period. The results presented in Table 3 are expressed on a body weight basis (g/kg/d), on a LBM basis (g/kg/LBM/d), and on a 24-hour

In the present study, we have evaluated a homogenous group of 32 patients with newly diagnosed advanced lung cancer (stage III and IV) in the postabsorptive state and before undergoing any radiation and/or chemotherapy treatment and compared them with 19 healthy volunteer control subjects of comparable age and weight. Compared with control subjects, patients with cancer had a 19% increase in WBPT and a 33% increase in WBPS when protein kinetics were expressed in terms of body weight. When protein kinetics were expressed in terms of LBM or creatinine excretion, subjects with cancer had a 14% to 15% increase in WBPT and a 24% to 29% increase in WBPS. The data presented in Table 2 demonstrate the relatively good comparison between lung cancer patients and control subjects in that age, height, weight, ideal body weight, body mass index, hematocrit, and, most importantly, LBM as determined by deuterium oxide dilution were not significantly different between the two groups. Although the mean percent stated weight loss in the cancer group was elevated as compared with that of the controls (8.1% v 2.6%) and the albumin level was depressed, suggesting mild malnutrition, none of the 32 advanced lung cancer patients were considered severely malnourished. The mean percent of ideal body weight for height was 96.4% * 4.0% in the cancer group. Only three cancer patients had experienced a Table 3. ‘5N-Glycine Whole-Body Protein Kinetic Data

Parameter

-

LungCancer In = 32)

Controls (n = 19)

P Value*

WBPTt g/kg/d

2.5 + 0.1

2.1 + 0.1

g/kg LBMld

3.3 2 0.2

2.9 + 0.2

,132

142.4 * 8.3

123.4 2 7.8

,127 ,026

g/g creatinine/d

,045

WBPS g/kg/d

1.6 + 0.1

1.2 -t 0.1

g/kg LBM/d

2.1 f 0.2

1.7 2 0.2

,056

94.9 r 8.3

73.4 + 8.0

,087

g/g creatinineid NPS g/kg/d

-0.8

2 0.1

-0.9

-t 0.1

,701

g/kg LBM/d

-1.1

2 0.1

-1.2

+ 0.1

,302

~47.4 ? 2.6

-50.0

+ 3.1

,525

g/g creatininejd

Abbreviation: NPS, net protein synthesis (WBPS - WBPT). *Unpaired Student’s t test for cancer patients v controls. tWBPT = WBPC since nitrogen intake equals zero.

PROTEIN TURNOVER IN ADVANCED

LUNG CANCER

clinically significant weight loss (> 15%) from their usual weight. When these three patients were omitted from the analysis. the stated weight loss of the cancer group decreased to 6.6% * 0.8%. Although this degree of weight loss suggests the onset of cancer cachexia, it is important to recognize that stated weight loss can be relatively inaccurate. RME data indicate that there was no significant differcncc between the two groups with regard to measured RME, and that the stage III to IV lung cancer patients in this study wcrc not hypermetabolic when compared with controls. In addition. muscle mass as assessed by 24-hour urinary creatinine excretion was identical between the men and women in each group; the rate of creatinine excretion is appropriate for subjects of this age. Bingham et ally rcportcd crcatinine excretion rates of 23.6 mgikgid for males and 18.4 mg/kg/d for females. Walser”” reported regression equations to adjust for the decrease in creatininc cxcrction that occurs with age; the age-adjusted rates are 18.3 mg/kgid for males and 15.2 mg/kg/d for females. Although prior nutritional intake was not quantitatively assessed. decreased food intake and the presence of anorexia were not evident in the lung cancer group. The 34-hour urinary nitrogen levels of 133.4 2 8.1 mgikgid in the cancer group and 139.7 t 9.0 mg/kg/d in the controls reflect normal nitrogen excretion levels in adult subjects. and provide no evidence of diminished prior nutrient intake or anorexia in the cancer patients. The only nutritional parameter that was perhaps suggestive of a decreased nutrient intake was the slightly decreased albumin level observed before any significant change in body composition in cancer patients. The volunteer subjects admitted to our clinical research unit and used as controls in this study were chosen because of their similarity to the cancer patients. In addition, both groups had similar smoking habits and respiratory function as determined by pulmonary function tests. Based on these similarities and the above indicators of comparable nutrition status, we feel that our homogenous lung cancer population without significant weight loss is best compared with a group of normal healthy control subjects with compar,able body composition and without weight loss. Our kinetic data presented in Table 3 indicate a signiticant increase in WBPT. WBPS, and WBPC when expressed on a total body weight basis in patients with newly diagnosed advanced lung cancer. However, when protein kinetic data arc normalized to either LBM or 24-hour urinary creatininc cxcrction, the observed increases in WBPT. WBPS, and WBPC are no longer significantly different from the controls. It is important to note that while WBPT, WBPS, WBPC in the cancer patients were not statistically different from those of the controls when expressed per kilogram LBM or per gram 24-hour urinary creatinine excretion, the actual mean values still demonstrated an increased trend in the cancer patients. This effect of expressing data on the basis of total body weight versus LBM has also been demonstrated in other studies addressing the effects of body composition on enera expenditurC,“mJ’

295

While the onset of cancer cachexia is closely associated with the presence of malignancy, correlations between the tumor primary site, disease stage, histology, and duration of illness arc not yet apparent.s,3J.J5 Currently, decreased nutrient intake, altered energy expenditure, and abnormal substrate utilization have been shown to exert a combined effect on the occurrence of cancer cachexia. Loss of LBM and depletion of protein reserves as evidenced by muscle wasting and decreases in plasma protein levels have been correlated with elevated rates of WBPT in several stud~cs.“-‘~ However. other studies report no increases in protein turnover.” lx These conflicting results are potentially due to methodological differences, heterogenous cancer patient populations, small study groups, varied nutritional regimens, different types of treatment, and, perhaps most importantly, the time with regard to disease progression at which cancer patients were evaluated. It has been suggested that increases in protein turnover may be due to the metastatic spread of the cancerjh.i7 and may only occur in fasting rather than fed subjects.ih.17 In addition to differences in experimental design and patient populations, most studies of protein kinetics report protein kinetic measurements on a total body weight basis rather than on a LBM basis. It has been suggested that the observed increases in WBPT in cancer patients may be in part due to increases in the proportion of lcan to fat tissue.” We have reported all measured protein kinetic values per kilogram total body weight, per kilogram LBM, and per gram 24-hour urinary crcatininc excretion to eliminate the potential effect of individual changes in body composition. Previous reports specifically evaluating whole-body protein kinetics in patients with lung cancer are few and suggest that WBPT is increased as compared with that of healthy control subjects. In a group of 12 fasting patients with non-oat-cell lung cancer, Heber et al” reported increased WBPT expressed on a total body weight basis as compared with six healthy control subjects. However. it is important to note that some of their patients had received a standardized chemotherapy regimen before study. In a more recent study of nine newly diagnosed patients with carcinoma of the lung in the fasted state, Melville et ali’ reported normal resting energy expenditures and increased rates of leucine flux, WBPS, and WBPC expressed per kilogram LBM. The results of our protein kinetic evaluation in a group of 32 postabsorptive lung cancer patients confirm an increase in WBPT as reported by Heber et al’ when expressed on a total body weight basis. However, they do not support the observation of Melville et al” of increased protein kinetics when data are expressed on the basis of kilogram LBM. While we do not dispute the contention that increases in WBPT contribute to the loss of LBM commonly associated with malignant neoplasms. our data suggest that the onset of such significant alterations in substrate metabolism may not occur until later in the disease process. It is important to note that while not statistically significant, WBPT and WBPS were increased in the present study regardless of how the data were expressed. This cycling of protein characterized by increased rates of protein catabolism and,

RICHARDS ET AL

296

to a lesser extent, synthesis may contribute to the loss of LBM. Our data demonstrate the extreme importance of expressing such protein kinetic measurements in terms of active muscle mass using either LBM or 24-hour creatinine excretion when dealing with patients who are likely to be experiencing changes in body composition. Furthermore, it is evident

that

longitudinal

assessment

of changes

in pro-

tein and energy metabolism in patients with cancer may reveal when and to what extent such changes occur. Such

studies are necessary before optimal nutritional intcrventions can be developed and used in the cancer patient. ACKNOWLEDGMENT The authors wish to acknowledge Kathy Martin, Alan Wayland. and Toni Conway for their technical assistance, Mohammad A. Khaled for consultation and deuterium oxide measurements, and

the nursing and technical support staff of the Baptist Medical Centers

in Birmingham,

AL.

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