Association of Severe Insulin Resistance With Both Loss of Limb Fat and Elevated Serum Tumor Necrosis Factor Receptor Levels in HIV Lipodystrophy
     full PDF version also available.
Dennis C. Mynarcik*;~ Margaret A. McNurlan;* Roy T. Steigbigel;* Jack Fuhrer;* Marie C. Gelato
     *Department of Medicine and ~Department of Surgery, State University of New York at Stony Brook, Stony Brook, New York, U.S.A.
     from the JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES 2000;25:312-321

HIV-lipodystrophy (HIV-LD) is characterized by the loss of body fat from the limbs and face, an increase in truncal fat, insulin resistance, and hyperlipidemia, factors placing affected patients at increased risk for vascular disease. This study evaluated insulin sensitivity and inflammatory status associated with HIV-LD and provides suggestions about its etiology. Insulin sensitivity and immune activation markers were assessed in 12 control subjects and 2 HIV-positive groups, 14 without and 15 with LD syndrome. Peripheral insulin sensitivity (mostly skeletal muscle) was determined with the hyperinsulinemic-euglycemic clamp. Circulating insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) and free fatty acid (FFA) levels, and their response to insulin infusion were indicative of insulin responsiveness of liver and adipose tissue, respectively. Serum levels of soluble type 2 tumor necrosis factor- (TNF-) receptor (sTNFR2) were used as an indicator of immune activation. HIV-LD study subjects had significantly reduced (twofold) peripheral insulin sensitivity, but normal levels of FFA and reduced levels of IGFBP-1, relative to the nonlipodystrophy groups, indicating that the loss of insulin sensitivity was more pronounced in skeletal muscle than in liver or fat. The significant loss of peripheral fat in the HIV-LD group (34%; p < .05) closely correlated with the reduced peripheral insulin sensitivity (p = .0001). Levels of sTNFR2 were elevated in all HIV-infected study subjects, but they were significantly higher in those with lipodystrophy than without, and sTNFR2 levels strongly correlated with the reduction in insulin sensitivity (p = .0001). Loss of peripheral fat, normal levels of FFA, and reduced levels of IGFBP-1 indicate that insulin resistance in HIV-LD is distinct from type 2 diabetes and obesity. The relationship between the degree of insulin resistance and sTNFR2 levels suggests an inflammatory stimulus is contributing to the development of HIV-associated lipodystrophy.

Multidrug regimens have changed the character of the pathology of HIV disease from lethal wasting, in many patients, to a managed clinical condition. However, increased survival has also been associated with a loss of fat from the face and the extremities and increased truncal fat, and dorsocervical fat ``buffalo hump'' (1-3), which has been described as a lipodystrophy syndrome. This redistribution of body fat is accompanied by metabolic perturbations including insulin resistance and hyperlipidemia, both hypertriglyceridemia and hypercholesterolemia (1,4), similar to metabolic syndrome X (5). The prevalence of HIV-lipodystrophy (HIV-LD) is reported to be as high as 50% (1,6). The impact of changes in body habitus for individuals, and the widespread occurrence qualify this syndrome as a major cause for concern. Although many studies have associated this syndrome with the use of HIV protease inhibitors (1,7-9), other evidence suggests that fat redistribution is occurring in patients who have not taken protease inhibitors (2) and, indeed, that it was occurring before the
introduction of protease inhibitors (10,11). Defining the etiology of the HIV-associated LD syndrome and its related metabolic abnormalities is an urgent priority.

In obesity and type 2 diabetes mellitus, two factors have been implicated in the etiology of insulin resistance. These factors are elevated free fatty acids (FFAs) and the cytokine tumor necrosis factor- (TNF-). In both obesity and type 2 diabetes, insulin resistance is associated with elevated levels of FFAs (5,12). Elevated FFA levels alone are sufficient to induce insulin
resistance without any underlying pathology (13,14), apparently by altering insulin signaling in skeletal muscle (15). Additional markers of insulin resistance include increased abdominal fat in obesity (16) and type 2 diabetes mellitus (17-19) and elevated serum levels of insulin-like growth factor binding protein-1 (IGFBP-1) (20).

Insulin resistance in obesity has been associated with a cytokine, TNF-, which is specifically implicated in the induction of insulin resistance (21) through inhibition of the insulin signaling cascade that regulates glucose uptake (22). The role of TNF- in the development of insulin resistance currently seen in HIV disease is not known. Cytokines, such as TNF-, were suspected in the wasting aspects of HIV infection, but low circulating levels failed to support this (23) (see also commentary by Grunfeld [24]), whereas cytokines did contribute to hepatic lipogenesis (25). With effective antiretroviral treatment, HIV-infected patients have improved disease control, as assessed by mortality (26), low to undetectable viral load, and increased numbers of CD4+ lymphocytes (27). The components of the TNF system are reduced in patients receiving highly active antiretroviral therapy (HAART) (28) but it would be instructive to know whether they remain depressed in HIV LD.

The present study was designed to characterize insulin resistance manifest in HIV patients who have the LD syndrome, but not overt diabetes, i.e., fasting, hyperglycemia. The degree of peripheral insulin resistance in these patients was assessed by the hyperinsulinemic-euglycemic clamp (29). This method suppresses hepatic glucose output and provides an accurate measurement of the rate of insulin-stimulated glucose disposal in skeletal muscle. Insulin resistance was related to physiologic parameters known to be altered in insulin resistant states, that is, body fat distribution (30,31), circulating levels of FFAs (32-34), and IGFBP-1 (20). In addition, serum levels of soluble type 2 TNF- receptor (sTNFR2) were assessed, inasmuch as elevated levels of sTNFR2 have not only been associated with the clinical course of HIV infection (35), but in particular were found to correlate with insulin resistance in obesity (36).

STUDY SUBJECTS AND METHODS

Those enrolled in the present study consisted of 12 healthy control study subjects, 14 study subjects infected with HIV without LD (denoted here as HIV), and 15 HIV-positive study subjects with the LD syndrome (HIV-LD). There were two exclusion criteria, diabetes, based on a random plasma glucose level >200 mg/dl or a fasting plasma glucose >126 mg/dl (based on diagnostic criteria in the Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, 1997), and acute illness within the 3 months preceding the study. HIV-LD study subjects had self-reported loss of fat from the limbs and face with accumulation of fat in the abdomen and trunk, which was confirmed by physician assessment at the time of study. Control study subjects were matched for age and gender with the HIV and the HIV-LD groups. The HIV group consisted of 7 patients who were asymptomatic, 3 patients with AIDS, and 4 patients with AIDS and a prior history of weight loss. The HIV-LD group consisted of 7 asymptomatic patients and 8 patients with AIDS.

Most HIV-infected study subjects were receiving multidrug regimens and continued these medications during the study. In the HIV group, all patients except 2 were taking nucleoside reverse transcriptase inhibitors, 2 were taking nonnucleoside reverse transcriptase inhibitors, and 11 were taking protease inhibitors. Similarly in the HIV-LD group, all except 1 patient were taking reverse transcriptase inhibitors, 3 were taking nonnucleoside reverse transcriptase inhibitors, and 13 were taking protease inhibitors. No difference was found in the degree of peripheral fat loss or insulin resistance in those patients taking protease
inhibitors and those who were not, although the number of patients who were not taking protease inhibitors was small.

DISCUSSION:
Unique Because Trunk Adiposity & Insulin Resistance Appears not to be Related to Fat Loss as in Type 2 Diabetes

In the present study, patients with clinically defined HIV LD had a 34%  reduction in percentage of limb fat, relative to findings in the control group (Table 1).
These These patients exhibited severe insulin resistance (Fig. 1) of a magnitude similar to that seen with type 2 diabetes mellitus (43,44).

 The loss of limb fat was highly correlated (p = .0001) with insulin resistance, as shown in Figure 2, demonstrating, for the first time, that insulin resistance accompanies the pathologic loss of peripheral fat.

The well recognized association between trunk adiposity and insulin resistance appears not to be a significant factor in HIV-LD. When patients with HIV-LD were stratified into groups with the greatest versus the least amount of trunk adipose tissue (19.0 kg versus 6.8 kg trunk fat), the two groups had similar insulin sensitivities (data not shown). An alarming feature of HIV-LD is that in the context of a routine clinic examination, the HIV-LD group may be unremarkable, with normal screening glucose levels (data not shown), and elevated triglyceride levels, a feature that has become an expected finding of HIV infection (45). The HIV-LD patients also had significantly elevated levels of the sTNFR2 (Fig. 3).

This finding is of interest, given that these patients are doing well clinically, with well-controlled HIV replication and improved numbers of CD4+ lymphocytes. Furthermore, insulin resistance in the HIV-infected population was highly correlated (p = .0001) with the serum levels of the sTNFR2 (Fig. 4), suggesting that inflammation may contribute to the pathophysiology of LD and insulin resistance.

 At present, the cellular source of the sTNFR2 is unknown, and investigations are currently under way to identify this source.

The clinical characteristics of HIV-LD bear a resemblance to the rare forms of acquired and congenital lipodystrophies (49-52), as well as an animal model of lipoatrophic diabetes (53). The congenital and acquired generalized lipodystrophies are characterized by loss of both trunk and limb fat, increased LBM (51), severe insulin resistance (52), normal levels of FFAs (51,52), and suppressed levels of IGFBP-1 (50). All these characteristics, except loss of trunk fat, are also shared with HIV-LD, suggesting that loss of peripheral fat alone may be sufficient to induce a state of peripheral insulin resistance. The increases in the LBM index of the HIV-LD group may also be causally linked to the LD syndrome.

Fat distribution, physiologic parameters, and serum markers associated with different insulin-resistant states are summarized in Table 2. These data demonstrate that the insulin resistance in HIV-LD is distinct from that associated with most forms of type 2 diabetes, based on hepatic insulin sensitivity, reflected by both fasting glycemia (Table 1) and IGFBP-1 levels (Fig. 5), and insulin sensitivity of adipose tissue reflected by fasting FFA levels (Fig. 5).

 The distinction between HIV-LD and obesity, although not so dramatic as with type 2 diabetes, is still clearly demonstrated by the differences in fasting FFA levels (Table 2). Table 2 also demonstrates that the insulin resistant state associated with HIV-LD has most in common with the exceedingly rare congenital and acquired lipodystrophies (52). The similarities include the loss of peripheral fat, increased LBM, severe insulin resistance, normal fasting FFA levels, and reduced IGFBP-1 levels. Although both increased trunk fat and elevated FFAs are commonly associated with insulin resistance, the presence of insulin resistance in acquired and congenital LD with loss of trunk fat and normal FFAs, suggests that loss of peripheral fat alone may also be sufficient to cause insulin resistance.

     A second paper by the same author.

Insulin-like Growth Factor System in Patients With HIV Infection: Effect of Exogenous Growth Hormone Administration
     Dennis C. Mynarcik*;* Robert A. Frost;~ Charles H. Lang;* Kim DeCristofaro;~ Margaret A. McNurlan;~ Peter J. Garlick;* Roy T. Steigbigel;* Jack Fuhrer;± Sang Ahnn;* Marie C. Gelato
     *Department of Medicine, ~Department of Surgery, and ±Department of Preventive Medicine, State University of New York at StonyBrook, StonyBrook, New York, U.S.A.
     R. A. Frost and C. H. Lang are currently affiliated with the Department of Cellular and Molecular Physiology, Pennsylvania State University, Hershey Medical Center, Hershey, Pennsylvania, U.S.A.
     from the JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES 1999;22:49

Summary:
The purpose of this study was to characterize changes in the levels of insulin-like growth factor-I (IGF-I) and IGF binding proteins (BP) 1, 2, and 3 in HIV-infected adults throughout the course of their disease, and to assess the responsiveness of the IGF system components to growth hormone (GH) administration (6 mg/day) for 2 weeks. Healthy control study subjects (n =10) were compared with patients who were either HIV-positive (n = 9), had AIDS without weight loss (n = 13), or had AIDS with >10% weight loss (n = 6), all of whom had been free of acute illness for at least 3 months.

Under basal conditions, fasting serum concentrations of epinephrine, norepinephrine, cortisol, glucagon, insulin, IGF-I, and IGFBP-3 were not significantly different among the four groups. The serum concentrations of IGFBP-1 and IGFBP-2 were significantly higher in AIDS patients with wasting than in the other three groups (p < .05). In addition, there was a statistically significant positive correlation between the levels of IGFBP-1 (p = .004) and IGFBP-2 (p = .03) and the stage of disease.

Following GH administration, the serum concentrations of insulin and IGF-I were increased in all groups (p < .05). In addition, the increases in insulin levels correlated with stage of disease (p = .004). The responses of the IGFBPs were more variable. GH administration significantly increased the levels of IGFBP-3 in all groups except the patients with AIDS wasting, whereas the levels of IGFBP-1 were significantly decreased in controls and AIDS patients. These results demonstrate that there is a continuum of both elevations in the IGFBPs and altered metabolic responsiveness in patients infected with HIV that increases with the severity of the disease. These data also demonstrate that AIDS patients, who are free from secondary infection, respond to administration of GH by significantly increasing hepatic IGF-I production.