Hyperlipidaemia is frequently associated with antiretroviral treatment and this has led to concerns about an increased cardiovascular risk in treated HIV-positive patients . The data on cardiovascular events in HIV-positive patients are anecdotal or retrospective and do not allow firm conclusions to be drawn regarding the influence of hyperlipidaemia associated with antiretroviral therapy on cardiovascular risk [2–4]. High-resolution ultrasound studies assessing intima media thickness and the presence of atherosclerotic plaques as signs of premature atherosclerosis are conflicting [5–7]. However, despite the lack of clear evidence, most clinicians assume that hyperlipidaemia associated with antiretroviral treatment does increase the cardiovascular risk, and treatment with lipid-lowering agents is common .
It has been shown that hypercholesterolaemia found in HIV-positive patients is frequently caused by the elevation of very low density lipoprotein (VLDL) [1,9–13]. Because of this, the proportion of hyperlipidaemia caused by VLDL in HIV-positive patients taking antiretroviral therapy is in excess of the proportion found in the general population. Two well-described genetically inherited lipid disorders that involve an increase in VLDL may serve as models to analyse further the lipoprotein pattern in HIV-positive patients with elevated VLDL and to estimate their cardiovascular risk. Familial combined hyperlipidaemia is caused by overproduction of small VLDL particles in the liver, leading to a parallel increase in apolipoprotein B and is associated with increased cardiovascular risk [14,15]. Familial hypertriglyceridaemia is characterized by production of normal numbers of large VLDL particles containing more triglycerides than normal. This results in normal apolipoprotein B levels and no or only modestly increased cardiovascular risk [16,17].
In the present study, lipoprotein patterns were analysed in HIV-positive patients with and without antiretroviral treatment, HIV-seronegative patients with familial combined hyperlipidaemia (high cardiovascular risk) or with familial hypertriglyceridaemia (low cardiovascular risk). In addition the size of VLDL particles were measured in a subgroup of HIV-positive patients who had Fredrickson type IV hyperlipidaemia and this was compared with that in those with the familial dyslipidaemias.
Fasting serum samples were drawn in the morning from 187 consecutive HIV-positive patients over a 4 week period in two private practices. The samples from 14 HIV-seronegative patients with familial hypertriglyceridaemia and 10 patients with combined familial hyperlipidaemia were analysed as controls.
Blood was drawn in ethylendiaminetetraacetic acid-containing tubes (patient in a sitting position, after 12 h of fasting). Plasma was obtained by centrifugation (20 min, 1500 × g, at room temperature). Cholesterol and triglyceride levels were measured enzymatically in the plasma and VLDL using an automated clinical chemistry analyser (Roche/Hitachi 902, Roche, Mannheim, Germany). All samples were measured in duplicate (variation coefficient < 3%). VLDL was prepared by ultracentrifugation for 24 h (d = 1.006 g/ml, 50 000 rpm, 4°C) using the Beckman Ti 50 rotor (Beckman Instruments, Palo Alto, California, USA). VLDL-cholesterol, VLDL-triglycerides and VLDL-apolipoprotein B were determined in the supernatant. VLDL-apolipoprotein B was measured using immunonephelometry (Nephelometer 100, Behringwerke, Marburg, Germany).
Total cholesterol, low density lipoprotein (LDL)-cholesterol, high density lipoprotein (HDL)-cholesterol, triglycerides, apolipoprotein A1 and B were determined in serum. VLDL was analysed for cholesterol, triglyceride and apolipoprotein B. Age, sex, CD4 cell count, CD8 cell count, clinical stage of HIV infection [according to the Centers for Disease Control (CDC) classification 1993], HIV RNA, body mass index and antiretroviral substances were recorded and used as parameters for the multivariate analysis.
For a grouped analysis of the antiretroviral therapy regimen, patients were assigned to three antiretroviral treatment groups as follows: the protease inhibitor group, where the regimen included one or several protease inhibitors plus one or several nucleoside reverse transcriptase inhibitors; the non-nucleoside reverse transcriptase inhibitor group, when the regimen contained one non-nucleoside reverse transcriptase inhibitor plus one or several nucleoside reverse transcriptase inhibitors; the nucleoside reverse transcriptase inhibitor group, who were treated with nucleoside reverse transcriptase inhibitors only. Patients treated with a combination containing a protease inhibitor and a non-nucleoside reverse transcriptase inhibitor were excluded from the study.
The Fredrickson classification of hyperlipoproteinaemias was used . Fredrickson type IIa is defined as LDL-cholesterol of > 160 mg/dl (4.13 mmol/l), type IIb as LDL-cholesterol > 160 mg/dl (4.13 mmol/l) and VLDL-cholesterol of > 35 mg/dl (0.90 mmol/l), and type IV as VLDL-cholesterol > 35 mg/dl (0.90 mmol/l) without an increase in LDL-cholesterol.
For statistical analysis, non-paired Wilcoxon rank-test and t-test were used. Multivariate analyses were performed using multiple logistic regression models with P < 0.1 for entry into the model and P < 0.05 for remaining in the model. Analyses were performed using SAS (The SAS System; SAS Institute, Cary, North Carolina, USA).
Of the 187 HIV-positive patients enrolled in the study, 32 patients (17%) were treatment-naive, 20 (11%) received nucleoside reverse transcriptase inhibitors only, 68 (36%) a regimen containing a non-nucleoside reverse transcriptase inhibitor, 64 (34%) a protease inhibitor containing regimen. Patient on nucleoside reverse transcriptase inhibitors only showed no difference in the distribution of symptomatic HIV infection according to the CDC classification compared with patients without antiretroviral treatment. Compared with HIV-positive patients who were not taking antiretroviral therapy, patients taking HIV protease inhibitors had more frequently a history of an AIDS-defining event and patients treated with non- nucleoside reverse transcriptase inhibitors had more frequently a history of a non-AIDS defining HIV-associated clinical event. The demographic parameters of the HIV-positive study population are shown in Table 1. The frequency of the specific antiretroviral drugs used in the different treatment groups is listed in Table 2.
Hypercholesterolaemia, defined as a fasting total cholesterol level of > 200 mg/dl (5.17 mmol/l), was found in 85/187 patients (45%). Elevated serum triglycerides of > 200 mg/dl (2.3 mmol/l) were found in 103/187 (55%) patients. The phenotypes of hyperlipidaemia according to Fredrickson classification are shown in Fig. 1. Of the 114 HIV-positive patients with hyperlipidaemia, 11/114 (10%) were type IIa (elevated LDL-cholesterol), 16/114 (14%) type IIb (elevated LDL- and VLDL-cholesterol) and 87/114 (76%) type IV (elevated VLDL-cholesterol). Eleven of the 187 patients had triglycerides > 800 mg/dl (9.2 mmol/l).
Protease inhibitor treatment resulted in elevated total cholesterol, LDL-cholesterol, HDL-cholesterol and triglycerides compared with patients without antiretroviral treatment. Non-nucleoside reverse transcriptase inhibitor treatment was associated with higher total cholesterol, LDL-cholesterol, HDL-cholesterol and apolipoprotein A1. Nucleoside reverse transcriptase inhibitor treatment was associated only with increased HDL-cholesterol (Table 3).
In a multivariate analysis, elevated total cholesterol was associated with age > 40 years (P = 0.004) and with treatment with ritonavir (P = 0.002), efavirenz (P = 0.007) or indinavir (P = 0.03). An elevated LDL-cholesterol was associated with treatment with fortovase (P = 0.02), indinavir (P = 0.02) or efavirenz (P = 0.04). Higher apolipoprotein B levels were associated with higher age (P = 0.02) and treatment with lopinavir (P = 0.03). An increased HDL-cholesterol was associated with female sex (P = 0.003) and treatment with didanosine (P = 0.01). Higher apolipoprotein A1 was associated with a higher CD4 cell count (P = 0.005) and showed a trend for treatment with efavirenz (P = 0.06). Hypertriglyceridaemia was associated with stavudine and abacavir treatment in a univariate analysis, but no variable survived in the multivariate model.
HDL-cholesterol in HIV-positive patients without antiretroviral treatment is generally lower than in the normal population . However antiretroviral treatment of any kind increased the HDL-cholesterol (Table 3). In addition, compared with patients with familial combined hyperlipidaemia and familial hypertriglyceridaemia, HIV-positive patients had higher HDL- cholesterol levels (Table 4).
Cardiovascular risk was assessed further by measuring the VLDL composition from 34 HIV-positive patients with type IV hyperlipidaemia (elevated VLDL-cholesterol). The size and the number of the VLDL particles was calculated from the ratio of VLDL-triglycerides to VLDL-apolipoprotein B in the VLDL fraction prepared by ultracetrifugation. Two different cohorts were used as controls. Patients with familial hypertriglyceridaemia show a normal number of large triglyceride-rich VLDL particles, resulting in a high ratio of VLDL-triglycerides to VLDL-apolipoprotein B. Patients with familial combined hyperlipidaemia, where the number of normally sized particles is increased, are characterized by a low ratio. In the HIV-positive patients, the ratio of VLDL-triglycerides to VLDL-apolipoprotein B was 16.2 ± 6.0 (range, 9.4–42.5). This ratio was not different from the ratio found in 14 patients with familial hypertriglyceridaemia, 16.9 ± 6.0 (range, 8.8–24.3; P = 0.61). In contrast, the ratio of VLDL-triglycerides to VLDL-apolipoprotein B in these two groups differed highly from the 10 patients with familial combined hyperlipidaemia, who had a ratio of 6.7 ± 1.0 (range, 5.3–8.5; P < 0.00001). The range of the individual measurements did not even show an overlap between familial combined hyperlipidaemia and the other two groups (Table 4). In addition, patients with familial combined hyperlipidaemia showed increased serum apolipoprotein B compared with patients with HIV-associated hyperlipidaemia or familial hypertriglyceridaemia (Table 4).
In accordance with previous reports, the present study showed higher cholesterol and lipid levels in association with antiretroviral therapy, particularly in patients treated with regimen containing a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor [19–23] In the multivariate analysis, some protease inhibitors and the non-nucleoside reverse transcriptase inhibitor efavirenz were associated with an increase in total cholesterol and LDL-cholesterol. Treatment with nucleoside reverse transcriptase inhibitors only seemed not to have a profound effect on the lipid profile. Interestingly, antiretroviral treatment was associated with an increase in HDL-cholesterol and, in those taking a non-nucleoside reverse transcriptase inhibitor, with increased apolipoprotein A1, which is associated with HDL-cholesterol. Such an effect has been reported for efavirenz and nevirapin as part of nucleoside reverse transcriptase inhibitor-based treatment [24,25].
Very high levels of triglycerides, which may present a significant risk for the development of acute pancreatitis, were observed in a considerable minority of this cohort and 6 of these 11 patients received ritonavir as part of their antiretroviral regimen.
The most common cause for high total cholesterol in HIV-positive patients taking antiretroviral therapy in this and other studies was elevated VLDL. As the lipid content of VLDL is 80% triglycerides and 20% cholesterol, the increased concentration of VLDL leads to an elevated total cholesterol. An interaction between sterol regulatory element-binding protein-1C, a key element in the regulation of lipogenesis, and antiretroviral drugs is one of the proposed mechanisms for this phenomenon [26,27]. Additional factors may be HIV infection itself or a genetic predisposition [27–30].
In the present study, less than a third of the patients with high total cholesterol had an elevated LDL-cholesterol. This may be a result of genetically transmitted hypercholesterolaemia (as in the normal population) or an increased catabolism of VLDL to LDL. An increase in LDL-cholesterol is associated with increased cardiovascular risk . The situation with increased VLDL-cholesterol is more complex, as highlighted by the two genetically determined hyperlipidaemias discussed: familial combined hyperlipidaemia and familial hypertriglyceridaemia. The former is associated with high cardiovascular risk through a secondary increase in LDL-cholesterol and apolipoprotein B, whereas familial hypertriglyceridaemia is asssociated with an only slightly increased cardiovascular risk and unchanged apolipoprotein B and LDL-cholesterol levels [14–16]. As shown in Table 4, the pattern of dyslipidaemia in HIV-positive patients taking antiretroviral therapy and with Fredrickson type IV dyslipoproteinaemia resembles familial hypertriglyceridaemia rather than familial combined hyperlipidaemia. The analysis of VLDL particle size indicated that the particles in HIV-positive patients were large, similar to those in patients with familial hypertriglyceridaemia. No overlap of particle size was found between the 34 HIV-positive patients and the patients with familial combined hyperlipidaemia.
In general, HDL-cholesterol, which is generally regarded as protective against cardiovascular events , is reported to be lower in HIV-infected individuals with or without antiretroviral treatment compared with the general population [32,33]. However, in the present study, antiretroviral treatment was associated with an increase in HDL-cholesterol in HIV-positive patients. In direct comparison, HDL-cholesterol levels in HIV-positive patients with elevated VLDL were significantly higher than in patients with familial combined hyperlipidaemia or even those with familial hypertriglyceridaemia.
These observations could suggest that the large subgroup of HIV-positive patients taking antiretroviral treatment and with hypercholesterolaemia caused by increased VLDL may have a lower cardiovascular risk than generally expected. A differentiated analysis of the lipoprotein pattern should be included in prospective studies assessing the cardiovascular risk of HIV-positive patients to test this hypothesis. However, the contribution of other important cardiovascular risk factors frequently found in HIV-positive patients taking antiretroviral treatment, such as insulin resistance, must also be considered in prospective studies.
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